On Thu, Dec 31, 2020 at 8:29 AM Bharath Rupireddy <bharath.rupireddyforpostg...@gmail.com> wrote: > Right. I meant the "next use" as the select attempt on a foreign table > with that foreign server. If no select query is run, then at the end > of the current txn that connection gets closed. Yes internally such > connection gets closed in pgfdw_xact_callback. > > If the errdetail("Such connections get closed either in the next use > or at the end of the current transaction.") looks confusing, how about > > 1) errdetail("Such connection gets discarded while closing the remote > transaction.")/errdetail("Such connections get discarded while closing > the remote transaction.") > 2) errdetail("Such connection is discarded at the end of remote > transaction.")/errdetail("Such connections are discarded at the end of > remote transaction.") > > I prefer 2) Thoughts? > > Because we already print a message in pgfdw_xact_callback - > elog(DEBUG3, "closing remote transaction on connection %p"
I changed the message to "Such connection is discarded at the end of remote transaction.". I'm attaching v5 patch set i.e. all the patches 0001 ( for new functions), 0002 ( for GUC) and 0003 (for server level option). I have also made the changes for increasing the version of postgres_fdw--1.0.sql from 1.0 to 1.1. I have no open points from my end. Please consider the v5 patch set for further review. With Regards, Bharath Rupireddy. EnterpriseDB: http://www.enterprisedb.com
From 413a8b34f8e1e1faf03aecad926a4b2a7a724aaa Mon Sep 17 00:00:00 2001 From: Bharath Rupireddy <bharath.rupireddy@enterprisedb.com> Date: Fri, 1 Jan 2021 14:09:54 +0530 Subject: [PATCH v5 1/3] postgres_fdw function to discard cached connections This patch introduces new function postgres_fdw_disconnect() when called with a foreign server name discards the associated connections with the server name. When called without any argument, discards all the existing cached connections. This patch also adds another function postgres_fdw_get_connections() to get the list of all cached connections by corresponding foreign server names. --- contrib/postgres_fdw/Makefile | 2 +- contrib/postgres_fdw/connection.c | 319 +++++++++++++- .../postgres_fdw/expected/postgres_fdw.out | 415 +++++++++++++++++- ...dw--1.0.sql => postgres_fdw--1.0--1.1.sql} | 6 +- contrib/postgres_fdw/postgres_fdw--1.1.sql | 33 ++ contrib/postgres_fdw/postgres_fdw.control | 2 +- contrib/postgres_fdw/sql/postgres_fdw.sql | 166 +++++++ doc/src/sgml/postgres-fdw.sgml | 57 ++- 8 files changed, 976 insertions(+), 24 deletions(-) rename contrib/postgres_fdw/{postgres_fdw--1.0.sql => postgres_fdw--1.0--1.1.sql} (60%) create mode 100644 contrib/postgres_fdw/postgres_fdw--1.1.sql diff --git a/contrib/postgres_fdw/Makefile b/contrib/postgres_fdw/Makefile index ee8a80a392..52d3dac0bd 100644 --- a/contrib/postgres_fdw/Makefile +++ b/contrib/postgres_fdw/Makefile @@ -14,7 +14,7 @@ PG_CPPFLAGS = -I$(libpq_srcdir) SHLIB_LINK_INTERNAL = $(libpq) EXTENSION = postgres_fdw -DATA = postgres_fdw--1.0.sql +DATA = postgres_fdw--1.1.sql postgres_fdw--1.0--1.1.sql REGRESS = postgres_fdw diff --git a/contrib/postgres_fdw/connection.c b/contrib/postgres_fdw/connection.c index d841cec39b..b9f6050f4b 100644 --- a/contrib/postgres_fdw/connection.c +++ b/contrib/postgres_fdw/connection.c @@ -22,6 +22,7 @@ #include "postgres_fdw.h" #include "storage/fd.h" #include "storage/latch.h" +#include "utils/builtins.h" #include "utils/datetime.h" #include "utils/hsearch.h" #include "utils/inval.h" @@ -57,6 +58,8 @@ typedef struct ConnCacheEntry bool have_error; /* have any subxacts aborted in this xact? */ bool changing_xact_state; /* xact state change in process */ bool invalidated; /* true if reconnect is pending */ + /* Server oid to get the associated foreign server name. */ + Oid serverid; uint32 server_hashvalue; /* hash value of foreign server OID */ uint32 mapping_hashvalue; /* hash value of user mapping OID */ } ConnCacheEntry; @@ -73,6 +76,12 @@ static unsigned int prep_stmt_number = 0; /* tracks whether any work is needed in callback functions */ static bool xact_got_connection = false; +/* + * SQL functions + */ +PG_FUNCTION_INFO_V1(postgres_fdw_get_connections); +PG_FUNCTION_INFO_V1(postgres_fdw_disconnect); + /* prototypes of private functions */ static void make_new_connection(ConnCacheEntry *entry, UserMapping *user); static PGconn *connect_pg_server(ForeignServer *server, UserMapping *user); @@ -94,6 +103,8 @@ static bool pgfdw_exec_cleanup_query(PGconn *conn, const char *query, static bool pgfdw_get_cleanup_result(PGconn *conn, TimestampTz endtime, PGresult **result); static bool UserMappingPasswordRequired(UserMapping *user); +static bool disconnect_cached_connections(uint32 hashvalue, bool all, + bool *is_in_use); /* * Get a PGconn which can be used to execute queries on the remote PostgreSQL @@ -273,6 +284,7 @@ make_new_connection(ConnCacheEntry *entry, UserMapping *user) entry->have_error = false; entry->changing_xact_state = false; entry->invalidated = false; + entry->serverid = server->serverid; entry->server_hashvalue = GetSysCacheHashValue1(FOREIGNSERVEROID, ObjectIdGetDatum(server->serverid)); @@ -789,6 +801,13 @@ pgfdw_xact_callback(XactEvent event, void *arg) if (!xact_got_connection) return; + /* + * Quick exit if the cache has been destroyed in + * disconnect_cached_connections. + */ + if (!ConnectionHash) + return; + /* * Scan all connection cache entries to find open remote transactions, and * close them. @@ -985,6 +1004,13 @@ pgfdw_subxact_callback(SubXactEvent event, SubTransactionId mySubid, if (!xact_got_connection) return; + /* + * Quick exit if the cache has been destroyed in + * disconnect_cached_connections. + */ + if (!ConnectionHash) + return; + /* * Scan all connection cache entries to find open remote subtransactions * of the current level, and close them. @@ -1093,6 +1119,13 @@ pgfdw_inval_callback(Datum arg, int cacheid, uint32 hashvalue) Assert(cacheid == FOREIGNSERVEROID || cacheid == USERMAPPINGOID); + /* + * Quick exit if the cache has been destroyed in + * disconnect_cached_connections. + */ + if (!ConnectionHash) + return; + /* ConnectionHash must exist already, if we're registered */ hash_seq_init(&scan, ConnectionHash); while ((entry = (ConnCacheEntry *) hash_seq_search(&scan))) @@ -1138,8 +1171,6 @@ pgfdw_inval_callback(Datum arg, int cacheid, uint32 hashvalue) static void pgfdw_reject_incomplete_xact_state_change(ConnCacheEntry *entry) { - HeapTuple tup; - Form_pg_user_mapping umform; ForeignServer *server; /* nothing to do for inactive entries and entries of sane state */ @@ -1150,13 +1181,7 @@ pgfdw_reject_incomplete_xact_state_change(ConnCacheEntry *entry) disconnect_pg_server(entry); /* find server name to be shown in the message below */ - tup = SearchSysCache1(USERMAPPINGOID, - ObjectIdGetDatum(entry->key)); - if (!HeapTupleIsValid(tup)) - elog(ERROR, "cache lookup failed for user mapping %u", entry->key); - umform = (Form_pg_user_mapping) GETSTRUCT(tup); - server = GetForeignServer(umform->umserver); - ReleaseSysCache(tup); + server = GetForeignServer(entry->serverid); ereport(ERROR, (errcode(ERRCODE_CONNECTION_EXCEPTION), @@ -1341,3 +1366,279 @@ exit: ; *result = last_res; return timed_out; } + +/* + * List the foreign server connections. + * + * This function takes no input parameter and returns an array with elements + * as pairs of foreign server name and true/false to show whether or not the + * connection is valid. The array elements look like (srv1, true), + * (srv2, false), (srv3, true) ... (srvn, true). True if the connection is + * valid. False if the connection is invalidated in pgfdw_inval_callback. NULL + * is returned when there are no cached connections at all. + * + * This function issues a warning in case for any connection the associated + * foreign server has been dropped which means that the server name can not be + * read from the system catalogues. + */ +Datum +postgres_fdw_get_connections(PG_FUNCTION_ARGS) +{ + ArrayBuildState *astate = NULL; + HASH_SEQ_STATUS scan; + ConnCacheEntry *entry; + StringInfoData buf; + uint16 no_server_conn_cnt = 0; + + if (!ConnectionHash) + PG_RETURN_NULL(); + + initStringInfo(&buf); + + hash_seq_init(&scan, ConnectionHash); + while ((entry = (ConnCacheEntry *) hash_seq_search(&scan))) + { + ForeignServer *server; + + /* We only look for open remote connections. */ + if (!entry->conn) + continue; + + server = GetForeignServerExtended(entry->serverid, true); + + /* + * The foreign server may have been dropped in the current explicit + * transaction. It's not possible to drop the server from another + * session when the connection associated with it is in use in the + * current transaction, if tried so the drop query in another session + * blocks until the current explicit transaction finishes. + * + * Even though the server is dropped in the current explicit + * transaction, the cache can have the associated active connection + * entry. Say we call such connections as dangling. Since we can not + * fetch the server name from system catalogues for dangling + * connections, instead we issue a warning. + * + * We could have done better by storing the server name in the cache + * entry instead of server oid so that it could be used in the output. + * But storing the server name in each cache entry requires 64bytes of + * memory, which is huge, considering the fact that there can exists + * many cached connections and the use case i.e. dropping the foreign + * server within the explicit current transaction seems rare. So, we + * chose to issue a warning instead. + * + * Such dangling connections get closed either in the next use or at + * the end of current explicit transaction in pgfdw_xact_callback. + */ + if (!server) + { + if (entry->conn) + { + /* + * If the server has been dropped in the current explicit + * transaction, then this entry would have been invalidated in + * pgfdw_inval_callback at the end of drop sever command. Note + * that this entry would not have been closed in + * pgfdw_inval_callback because it is still being used in the + * current explicit transaction. So, assert that here. + */ + Assert(entry->xact_depth > 0 && entry->invalidated); + + no_server_conn_cnt++; + } + + continue; + } + + appendStringInfo(&buf, "(%s, %s)", server->servername, + entry->invalidated ? "false" : "true"); + + /* stash away the prepared string into array value */ + astate = accumArrayResult(astate, CStringGetTextDatum(buf.data), + false, TEXTOID, CurrentMemoryContext); + resetStringInfo(&buf); + } + + if (no_server_conn_cnt > 0) + { + ereport(WARNING, + (errmsg_plural("found an active connection for which the foreign server would have been dropped", + "found some active connections for which the foreign servers would have been dropped", + no_server_conn_cnt), + no_server_conn_cnt > 1 ? + errdetail("Such connections are discarded at the end of remote transaction.") + : errdetail("Such connection is discarded at the end of remote transaction."))); + } + + if (astate) + PG_RETURN_ARRAYTYPE_P(makeArrayResult(astate, + CurrentMemoryContext)); + else + PG_RETURN_NULL(); +} + +/* + * Disconnect the cached connections. + * + * If server name is provided as input, this function disconnects the + * associated cached connection. Otherwise all the cached connections are + * disconnected. The cache can be destroyed when there are no active + * connections left. + * + * This function returns false if the cache doesn't exist. + * When the cache exists: + * 1) If the server name is provided, it first checks whether the foreign + * server exists, if not, an error is emitted. Otherwise it disconnects the + * associated connection when it's not being used in current transaction + * and returns true. If it's in use, then issues a warning and returns + * false. + * 2) If no input argument is provided, then it tries to disconnect all the + * connections. If all the connections are not being used, then it + * disconnects them and returns true. If all the connections are being + * used, then it issues a warning and returns false. If at least one + * connection is closed and others are in use, then issues a warning and + * returns true. + */ +Datum +postgres_fdw_disconnect(PG_FUNCTION_ARGS) +{ + bool result = false; + bool is_in_use = false; + + if (!ConnectionHash) + PG_RETURN_BOOL(result); + + if (PG_NARGS() == 1) + { + char *servername = NULL; + ForeignServer *server = NULL; + + servername = text_to_cstring(PG_GETARG_TEXT_PP(0)); + server = GetForeignServerByName(servername, true); + + if (server) + { + uint32 hashvalue; + + hashvalue = + GetSysCacheHashValue1(FOREIGNSERVEROID, + ObjectIdGetDatum(server->serverid)); + + result = disconnect_cached_connections(hashvalue, false, + &is_in_use); + } + else + ereport(ERROR, + (errcode(ERRCODE_CONNECTION_DOES_NOT_EXIST), + errmsg("foreign server \"%s\" does not exist", servername))); + + /* + * Check if the connection associated with the given foreign server is + * in use i.e. entry->xact_depth > 0. Since we can not close it, so + * error out. + */ + if (is_in_use) + ereport(WARNING, + (errmsg("cannot close the connection because it is still in use"))); + } + else + { + result = disconnect_cached_connections(0, true, &is_in_use); + + /* + * Check if some or all of the connections are in use i.e. + * entry->xact_depth > 0. Since we can not close them, so inform the + * user. + */ + if (is_in_use) + { + if (result) + { + /* We closed at least one connection. Others are in use. */ + ereport(WARNING, + (errmsg("cannot close all connections because some of them are still in use"))); + } + else + { + /* We did not closed any connection, all are in use. */ + ereport(WARNING, + (errmsg("cannot close any connection because they are still in use"))); + } + } + } + + PG_RETURN_BOOL(result); +} + +/* + * Workhorse to disconnect the cached connections. + * + * This function tries to disconnect the connections only when they are not in + * use in the current transaction. + * + * If all is true, all the cached connections that are not being used in the + * current transaction are disconnected. Otherwise, the unused entries with the + * given hashvalue are disconnected. + * + * This function destroys the cache when there are no active connections. And + * set is_in_use flag to true when there exists at least one connection that's + * being used in the current transaction. + * + * This function returns true in the following cases if at least one connection + * is disconnected. Otherwise it returns false. + */ +static bool +disconnect_cached_connections(uint32 hashvalue, bool all, bool *is_in_use) +{ + bool result = false; + HASH_SEQ_STATUS scan; + ConnCacheEntry *entry; + bool active_conn_exists = false; + + /* We are here only when ConnectionHash exists. */ + Assert(ConnectionHash); + + hash_seq_init(&scan, ConnectionHash); + while ((entry = (ConnCacheEntry *) hash_seq_search(&scan))) + { + /* + * Either disconnect given or all the active and not in use cached + * connections. + */ + if ((all || entry->server_hashvalue == hashvalue) && + entry->conn) + { + if (entry->xact_depth > 0) + *is_in_use = true; + else + { + elog(DEBUG3, "discarding connection %p", entry->conn); + disconnect_pg_server(entry); + result = true; + } + } + + /* + * If at least one active connection exists in the cache, mark it so + * that we don't destroy the cache. + */ + if (entry->conn && !active_conn_exists) + active_conn_exists = true; + } + + /* + * Destroy the cache if we discarded all the active connections i.e. if + * there is no single active connection, which we can know while scanning + * the cached entries in the above loop. Destroying the cache is better + * than to keep it in the memory with all inactive entries in it to save + * some memory. Cache can get initialized on the subsequent queries to + * foreign server. + */ + if (!active_conn_exists) + { + hash_destroy(ConnectionHash); + ConnectionHash = NULL; + } + + return result; +} diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out index c11092f8cc..ba29bc6131 100644 --- a/contrib/postgres_fdw/expected/postgres_fdw.out +++ b/contrib/postgres_fdw/expected/postgres_fdw.out @@ -13,12 +13,22 @@ DO $d$ OPTIONS (dbname '$$||current_database()||$$', port '$$||current_setting('port')||$$' )$$; + EXECUTE $$CREATE SERVER temploopback1 FOREIGN DATA WRAPPER postgres_fdw + OPTIONS (dbname '$$||current_database()||$$', + port '$$||current_setting('port')||$$' + )$$; + EXECUTE $$CREATE SERVER temploopback2 FOREIGN DATA WRAPPER postgres_fdw + OPTIONS (dbname '$$||current_database()||$$', + port '$$||current_setting('port')||$$' + )$$; END; $d$; CREATE USER MAPPING FOR public SERVER testserver1 OPTIONS (user 'value', password 'value'); CREATE USER MAPPING FOR CURRENT_USER SERVER loopback; CREATE USER MAPPING FOR CURRENT_USER SERVER loopback2; +CREATE USER MAPPING FOR public SERVER temploopback1; +CREATE USER MAPPING FOR public SERVER temploopback2; -- =================================================================== -- create objects used through FDW loopback server -- =================================================================== @@ -129,6 +139,16 @@ CREATE FOREIGN TABLE ft6 ( c2 int NOT NULL, c3 text ) SERVER loopback2 OPTIONS (schema_name 'S 1', table_name 'T 4'); +CREATE FOREIGN TABLE templbtbl1 ( + c1 int NOT NULL, + c2 int NOT NULL, + c3 text +) SERVER temploopback1 OPTIONS (schema_name 'S 1', table_name 'T 4'); +CREATE FOREIGN TABLE templbtbl2 ( + c1 int NOT NULL, + c2 int NOT NULL, + c3 text +) SERVER temploopback2 OPTIONS (schema_name 'S 1', table_name 'T 4'); -- =================================================================== -- tests for validator -- =================================================================== @@ -191,15 +211,17 @@ ALTER FOREIGN TABLE ft2 OPTIONS (schema_name 'S 1', table_name 'T 1'); ALTER FOREIGN TABLE ft1 ALTER COLUMN c1 OPTIONS (column_name 'C 1'); ALTER FOREIGN TABLE ft2 ALTER COLUMN c1 OPTIONS (column_name 'C 1'); \det+ - List of foreign tables - Schema | Table | Server | FDW options | Description ---------+-------+-----------+---------------------------------------+------------- - public | ft1 | loopback | (schema_name 'S 1', table_name 'T 1') | - public | ft2 | loopback | (schema_name 'S 1', table_name 'T 1') | - public | ft4 | loopback | (schema_name 'S 1', table_name 'T 3') | - public | ft5 | loopback | (schema_name 'S 1', table_name 'T 4') | - public | ft6 | loopback2 | (schema_name 'S 1', table_name 'T 4') | -(5 rows) + List of foreign tables + Schema | Table | Server | FDW options | Description +--------+------------+---------------+---------------------------------------+------------- + public | ft1 | loopback | (schema_name 'S 1', table_name 'T 1') | + public | ft2 | loopback | (schema_name 'S 1', table_name 'T 1') | + public | ft4 | loopback | (schema_name 'S 1', table_name 'T 3') | + public | ft5 | loopback | (schema_name 'S 1', table_name 'T 4') | + public | ft6 | loopback2 | (schema_name 'S 1', table_name 'T 4') | + public | templbtbl1 | temploopback1 | (schema_name 'S 1', table_name 'T 4') | + public | templbtbl2 | temploopback2 | (schema_name 'S 1', table_name 'T 4') | +(7 rows) -- Test that alteration of server options causes reconnection -- Remote's errors might be non-English, so hide them to ensure stable results @@ -9053,3 +9075,378 @@ SELECT 1 FROM ft1 LIMIT 1; ALTER SERVER loopback OPTIONS (ADD use_remote_estimate 'off'); -- The invalid connection gets closed in pgfdw_xact_callback during commit. COMMIT; +-- ======================================================================== +-- Test postgres_fdw_get_connections and postgres_fdw_disconnect functions +-- ======================================================================== +-- postgres_fdw_get_connections returns an array with elements in a +-- machine-dependent ordering, so we must resort to unnesting and sorting for a +-- stable result. +CREATE FUNCTION fdw_unnest(anyarray) RETURNS SETOF anyelement +LANGUAGE SQL STRICT IMMUTABLE AS $$ +SELECT $1[i] FROM generate_series(array_lower($1,1), array_upper($1,1)) AS i +$$; +-- Ensure to have loopback and loopback2 connections cached. +SELECT 1 FROM ft1 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +SELECT 1 FROM ft6 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +-- List all the existing cached connections. Should return loopback, loopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +------------------- + (loopback2, true) + (loopback, true) +(2 rows) + +-- loopback connection is disconnected. loopback2 connection still exists. +SELECT postgres_fdw_disconnect('loopback'); /* TRUE */ + postgres_fdw_disconnect +------------------------- + t +(1 row) + +-- List all the existing cached connections. Should return loopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +------------------- + (loopback2, true) +(1 row) + +-- Cache exists, but the loopback connection is not present in it. +SELECT postgres_fdw_disconnect('loopback'); /* FALSE */ + postgres_fdw_disconnect +------------------------- + f +(1 row) + +-- Cache exists, but the server name provided doesn't exist. +SELECT postgres_fdw_disconnect('unknownserver'); /* ERROR */ +ERROR: foreign server "unknownserver" does not exist +-- Cache and loopback2 connection exist, so discard it. +SELECT postgres_fdw_disconnect(); /* TRUE */ + postgres_fdw_disconnect +------------------------- + t +(1 row) + +-- Cache does not exist. +SELECT postgres_fdw_disconnect(); /* FALSE */ + postgres_fdw_disconnect +------------------------- + f +(1 row) + +-- Test the functions inside explicit xact. +-- Connections are being used in the xact, so they cannot be disconnected. +BEGIN; +SELECT 1 FROM templbtbl1 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +SELECT 1 FROM templbtbl2 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +-- Should output temploopback1, temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +----------------------- + (temploopback1, true) + (temploopback2, true) +(2 rows) + +SELECT * FROM postgres_fdw_disconnect('temploopback1'); /* WARNING and FALSE */ +WARNING: cannot close the connection because it is still in use + postgres_fdw_disconnect +------------------------- + f +(1 row) + +SELECT * FROM postgres_fdw_disconnect(); /* WARNING and FALSE */ +WARNING: cannot close any connection because they are still in use + postgres_fdw_disconnect +------------------------- + f +(1 row) + +-- Should output temploopback1, temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +----------------------- + (temploopback1, true) + (temploopback2, true) +(2 rows) + +COMMIT; +-- Should disconnect temploopback1, temploopback2. +SELECT * FROM postgres_fdw_disconnect(); /* TRUE */ + postgres_fdw_disconnect +------------------------- + t +(1 row) + +-- Connections can be closed in the xact because they are not in use. +SELECT 1 FROM templbtbl1 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +SELECT 1 FROM templbtbl2 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +BEGIN; +-- Should output temploopback1, temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +----------------------- + (temploopback1, true) + (temploopback2, true) +(2 rows) + +SELECT * FROM postgres_fdw_disconnect(); /* TRUE */ + postgres_fdw_disconnect +------------------------- + t +(1 row) + +-- Should return nothing. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +------------ +(0 rows) + +COMMIT; +-- temploopback1 connection is closed and temploopback2 is not, because it's +-- being used in the xact. +SELECT 1 FROM templbtbl1 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +BEGIN; +SELECT 1 FROM templbtbl2 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +-- Should output temploopback1, temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +----------------------- + (temploopback1, true) + (temploopback2, true) +(2 rows) + +SELECT * FROM postgres_fdw_disconnect('temploopback1'); /* TRUE */ + postgres_fdw_disconnect +------------------------- + t +(1 row) + +-- Should output temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +----------------------- + (temploopback2, true) +(1 row) + +COMMIT; +-- Should disconnect temploopback2. +SELECT * FROM postgres_fdw_disconnect(); /* TRUE */ + postgres_fdw_disconnect +------------------------- + t +(1 row) + +-- temploopback1 connection is closed and temploopback2 is not, because it's +-- being used in the xact. +SELECT 1 FROM templbtbl1 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +BEGIN; +SELECT 1 FROM templbtbl2 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +-- Should output temploopback1, temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +----------------------- + (temploopback1, true) + (temploopback2, true) +(2 rows) + +SELECT * FROM postgres_fdw_disconnect(); /* WARNING and TRUE */ +WARNING: cannot close all connections because some of them are still in use + postgres_fdw_disconnect +------------------------- + t +(1 row) + +-- Should output temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +----------------------- + (temploopback2, true) +(1 row) + +COMMIT; +-- Should disconnect temploopback2. +SELECT * FROM postgres_fdw_disconnect(); /* TRUE */ + postgres_fdw_disconnect +------------------------- + t +(1 row) + +-- temploopback1 connection is invalidated and temploopback2 is not. +BEGIN; +SELECT 1 FROM templbtbl1 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +SELECT 1 FROM templbtbl2 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +ALTER SERVER temploopback1 OPTIONS (ADD use_remote_estimate 'off'); +-- Should output temploopback1 as invalid, temploopback2 as valid. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +------------------------ + (temploopback1, false) + (temploopback2, true) +(2 rows) + +COMMIT; +-- Invalidated connection i.e. temploopback1 was closed at the end of the xact. +-- Should output temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +----------------------- + (temploopback2, true) +(1 row) + +-- Should disconnect temploopback2. +SELECT * FROM postgres_fdw_disconnect(); /* TRUE */ + postgres_fdw_disconnect +------------------------- + t +(1 row) + +-- Both temploopback1 and temploopback2 connections are invalidated. +BEGIN; +SELECT 1 FROM templbtbl1 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +SELECT 1 FROM templbtbl2 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +ALTER SERVER temploopback1 OPTIONS (SET use_remote_estimate 'off'); +ALTER SERVER temploopback2 OPTIONS (ADD use_remote_estimate 'off'); +-- Should output both temploopback1 and temploopback2 as invalid. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +------------------------ + (temploopback1, false) + (temploopback2, false) +(2 rows) + +COMMIT; +-- Invalidated connections i.e. temploopback1 and temploopback2 were closed at +-- the end of the xact. Should output nothing. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +------------ +(0 rows) + +-- No active connections. +SELECT * FROM postgres_fdw_disconnect(); /* FALSE */ + postgres_fdw_disconnect +------------------------- + f +(1 row) + +-- Both the servers were dropped inside the xact block, so a warning is +-- emitted. +BEGIN; +SELECT 1 FROM templbtbl1 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +SELECT 1 FROM templbtbl2 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +-- Should output temploopback1, temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +----------------------- + (temploopback1, true) + (temploopback2, true) +(2 rows) + +DROP SERVER temploopback1 CASCADE; +NOTICE: drop cascades to 2 other objects +DETAIL: drop cascades to user mapping for public on server temploopback1 +drop cascades to foreign table templbtbl1 +-- Should output temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; /* WARNING */ +WARNING: found an active connection for which the foreign server would have been dropped +DETAIL: Such connection is discarded at the end of remote transaction. + fdw_unnest +----------------------- + (temploopback2, true) +(1 row) + +DROP SERVER temploopback2 CASCADE; +NOTICE: drop cascades to 2 other objects +DETAIL: drop cascades to user mapping for public on server temploopback2 +drop cascades to foreign table templbtbl2 +-- Should output nothing. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; /* WARNING */ +WARNING: found some active connections for which the foreign servers would have been dropped +DETAIL: Such connections are discarded at the end of remote transaction. + fdw_unnest +------------ +(0 rows) + +COMMIT; +-- Clean up. +DROP FUNCTION fdw_unnest; diff --git a/contrib/postgres_fdw/postgres_fdw--1.0.sql b/contrib/postgres_fdw/postgres_fdw--1.0--1.1.sql similarity index 60% rename from contrib/postgres_fdw/postgres_fdw--1.0.sql rename to contrib/postgres_fdw/postgres_fdw--1.0--1.1.sql index a0f0fc1bf4..fa8d12d3e3 100644 --- a/contrib/postgres_fdw/postgres_fdw--1.0.sql +++ b/contrib/postgres_fdw/postgres_fdw--1.0--1.1.sql @@ -1,7 +1,7 @@ -/* contrib/postgres_fdw/postgres_fdw--1.0.sql */ +/* contrib/postgres_fdw/postgres_fdw--1.0--1.1.sql */ --- complain if script is sourced in psql, rather than via CREATE EXTENSION -\echo Use "CREATE EXTENSION postgres_fdw" to load this file. \quit +-- complain if script is sourced in psql, rather than via ALTER EXTENSION +\echo Use "ALTER EXTENSION postgres_fdw UPDATE TO '1.1'" to load this file. \quit CREATE FUNCTION postgres_fdw_handler() RETURNS fdw_handler diff --git a/contrib/postgres_fdw/postgres_fdw--1.1.sql b/contrib/postgres_fdw/postgres_fdw--1.1.sql new file mode 100644 index 0000000000..8a1453a495 --- /dev/null +++ b/contrib/postgres_fdw/postgres_fdw--1.1.sql @@ -0,0 +1,33 @@ +/* contrib/postgres_fdw/postgres_fdw--1.1.sql */ + +-- complain if script is sourced in psql, rather than via CREATE EXTENSION +\echo Use "CREATE EXTENSION postgres_fdw" to load this file. \quit + +CREATE FUNCTION postgres_fdw_handler() +RETURNS fdw_handler +AS 'MODULE_PATHNAME' +LANGUAGE C STRICT; + +CREATE FUNCTION postgres_fdw_validator(text[], oid) +RETURNS void +AS 'MODULE_PATHNAME' +LANGUAGE C STRICT; + +CREATE FOREIGN DATA WRAPPER postgres_fdw + HANDLER postgres_fdw_handler + VALIDATOR postgres_fdw_validator; + +CREATE FUNCTION postgres_fdw_get_connections () +RETURNS text[] +AS 'MODULE_PATHNAME','postgres_fdw_get_connections' +LANGUAGE C STRICT PARALLEL RESTRICTED; + +CREATE FUNCTION postgres_fdw_disconnect () +RETURNS bool +AS 'MODULE_PATHNAME','postgres_fdw_disconnect' +LANGUAGE C STRICT PARALLEL RESTRICTED; + +CREATE FUNCTION postgres_fdw_disconnect (text) +RETURNS bool +AS 'MODULE_PATHNAME','postgres_fdw_disconnect' +LANGUAGE C STRICT PARALLEL RESTRICTED; diff --git a/contrib/postgres_fdw/postgres_fdw.control b/contrib/postgres_fdw/postgres_fdw.control index f9ed490752..d489382064 100644 --- a/contrib/postgres_fdw/postgres_fdw.control +++ b/contrib/postgres_fdw/postgres_fdw.control @@ -1,5 +1,5 @@ # postgres_fdw extension comment = 'foreign-data wrapper for remote PostgreSQL servers' -default_version = '1.0' +default_version = '1.1' module_pathname = '$libdir/postgres_fdw' relocatable = true diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql index 25dbc08b98..2267aee630 100644 --- a/contrib/postgres_fdw/sql/postgres_fdw.sql +++ b/contrib/postgres_fdw/sql/postgres_fdw.sql @@ -15,6 +15,14 @@ DO $d$ OPTIONS (dbname '$$||current_database()||$$', port '$$||current_setting('port')||$$' )$$; + EXECUTE $$CREATE SERVER temploopback1 FOREIGN DATA WRAPPER postgres_fdw + OPTIONS (dbname '$$||current_database()||$$', + port '$$||current_setting('port')||$$' + )$$; + EXECUTE $$CREATE SERVER temploopback2 FOREIGN DATA WRAPPER postgres_fdw + OPTIONS (dbname '$$||current_database()||$$', + port '$$||current_setting('port')||$$' + )$$; END; $d$; @@ -22,6 +30,8 @@ CREATE USER MAPPING FOR public SERVER testserver1 OPTIONS (user 'value', password 'value'); CREATE USER MAPPING FOR CURRENT_USER SERVER loopback; CREATE USER MAPPING FOR CURRENT_USER SERVER loopback2; +CREATE USER MAPPING FOR public SERVER temploopback1; +CREATE USER MAPPING FOR public SERVER temploopback2; -- =================================================================== -- create objects used through FDW loopback server @@ -142,6 +152,17 @@ CREATE FOREIGN TABLE ft6 ( c3 text ) SERVER loopback2 OPTIONS (schema_name 'S 1', table_name 'T 4'); +CREATE FOREIGN TABLE templbtbl1 ( + c1 int NOT NULL, + c2 int NOT NULL, + c3 text +) SERVER temploopback1 OPTIONS (schema_name 'S 1', table_name 'T 4'); + +CREATE FOREIGN TABLE templbtbl2 ( + c1 int NOT NULL, + c2 int NOT NULL, + c3 text +) SERVER temploopback2 OPTIONS (schema_name 'S 1', table_name 'T 4'); -- =================================================================== -- tests for validator -- =================================================================== @@ -2711,3 +2732,148 @@ SELECT 1 FROM ft1 LIMIT 1; ALTER SERVER loopback OPTIONS (ADD use_remote_estimate 'off'); -- The invalid connection gets closed in pgfdw_xact_callback during commit. COMMIT; + +-- ======================================================================== +-- Test postgres_fdw_get_connections and postgres_fdw_disconnect functions +-- ======================================================================== + +-- postgres_fdw_get_connections returns an array with elements in a +-- machine-dependent ordering, so we must resort to unnesting and sorting for a +-- stable result. +CREATE FUNCTION fdw_unnest(anyarray) RETURNS SETOF anyelement +LANGUAGE SQL STRICT IMMUTABLE AS $$ +SELECT $1[i] FROM generate_series(array_lower($1,1), array_upper($1,1)) AS i +$$; + +-- Ensure to have loopback and loopback2 connections cached. +SELECT 1 FROM ft1 LIMIT 1; +SELECT 1 FROM ft6 LIMIT 1; + +-- List all the existing cached connections. Should return loopback, loopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + +-- loopback connection is disconnected. loopback2 connection still exists. +SELECT postgres_fdw_disconnect('loopback'); /* TRUE */ + +-- List all the existing cached connections. Should return loopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + +-- Cache exists, but the loopback connection is not present in it. +SELECT postgres_fdw_disconnect('loopback'); /* FALSE */ + +-- Cache exists, but the server name provided doesn't exist. +SELECT postgres_fdw_disconnect('unknownserver'); /* ERROR */ + +-- Cache and loopback2 connection exist, so discard it. +SELECT postgres_fdw_disconnect(); /* TRUE */ + +-- Cache does not exist. +SELECT postgres_fdw_disconnect(); /* FALSE */ + +-- Test the functions inside explicit xact. +-- Connections are being used in the xact, so they cannot be disconnected. +BEGIN; +SELECT 1 FROM templbtbl1 LIMIT 1; +SELECT 1 FROM templbtbl2 LIMIT 1; +-- Should output temploopback1, temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; +SELECT * FROM postgres_fdw_disconnect('temploopback1'); /* WARNING and FALSE */ +SELECT * FROM postgres_fdw_disconnect(); /* WARNING and FALSE */ +-- Should output temploopback1, temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; +COMMIT; + +-- Should disconnect temploopback1, temploopback2. +SELECT * FROM postgres_fdw_disconnect(); /* TRUE */ + +-- Connections can be closed in the xact because they are not in use. +SELECT 1 FROM templbtbl1 LIMIT 1; +SELECT 1 FROM templbtbl2 LIMIT 1; +BEGIN; +-- Should output temploopback1, temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; +SELECT * FROM postgres_fdw_disconnect(); /* TRUE */ +-- Should return nothing. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; +COMMIT; + +-- temploopback1 connection is closed and temploopback2 is not, because it's +-- being used in the xact. +SELECT 1 FROM templbtbl1 LIMIT 1; +BEGIN; +SELECT 1 FROM templbtbl2 LIMIT 1; +-- Should output temploopback1, temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; +SELECT * FROM postgres_fdw_disconnect('temploopback1'); /* TRUE */ +-- Should output temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; +COMMIT; + +-- Should disconnect temploopback2. +SELECT * FROM postgres_fdw_disconnect(); /* TRUE */ + +-- temploopback1 connection is closed and temploopback2 is not, because it's +-- being used in the xact. +SELECT 1 FROM templbtbl1 LIMIT 1; +BEGIN; +SELECT 1 FROM templbtbl2 LIMIT 1; +-- Should output temploopback1, temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; +SELECT * FROM postgres_fdw_disconnect(); /* WARNING and TRUE */ +-- Should output temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; +COMMIT; + +-- Should disconnect temploopback2. +SELECT * FROM postgres_fdw_disconnect(); /* TRUE */ + +-- temploopback1 connection is invalidated and temploopback2 is not. +BEGIN; +SELECT 1 FROM templbtbl1 LIMIT 1; +SELECT 1 FROM templbtbl2 LIMIT 1; +ALTER SERVER temploopback1 OPTIONS (ADD use_remote_estimate 'off'); +-- Should output temploopback1 as invalid, temploopback2 as valid. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; +COMMIT; + +-- Invalidated connection i.e. temploopback1 was closed at the end of the xact. +-- Should output temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + +-- Should disconnect temploopback2. +SELECT * FROM postgres_fdw_disconnect(); /* TRUE */ + +-- Both temploopback1 and temploopback2 connections are invalidated. +BEGIN; +SELECT 1 FROM templbtbl1 LIMIT 1; +SELECT 1 FROM templbtbl2 LIMIT 1; +ALTER SERVER temploopback1 OPTIONS (SET use_remote_estimate 'off'); +ALTER SERVER temploopback2 OPTIONS (ADD use_remote_estimate 'off'); +-- Should output both temploopback1 and temploopback2 as invalid. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; +COMMIT; + +-- Invalidated connections i.e. temploopback1 and temploopback2 were closed at +-- the end of the xact. Should output nothing. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + +-- No active connections. +SELECT * FROM postgres_fdw_disconnect(); /* FALSE */ + +-- Both the servers were dropped inside the xact block, so a warning is +-- emitted. +BEGIN; +SELECT 1 FROM templbtbl1 LIMIT 1; +SELECT 1 FROM templbtbl2 LIMIT 1; +-- Should output temploopback1, temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; +DROP SERVER temploopback1 CASCADE; +-- Should output temploopback2. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; /* WARNING */ +DROP SERVER temploopback2 CASCADE; +-- Should output nothing. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; /* WARNING */ +COMMIT; + +-- Clean up. +DROP FUNCTION fdw_unnest; diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml index e6fd2143c1..405923f2aa 100644 --- a/doc/src/sgml/postgres-fdw.sgml +++ b/doc/src/sgml/postgres-fdw.sgml @@ -477,7 +477,47 @@ OPTIONS (ADD password_required 'false'); </para> </sect3> - </sect2> + +<sect2> + <title>Functions</title> + + <para> + <function>postgres_fdw_get_connections</function> ( ) which takes no input. + When called in the local session, it returns an array with each element as a + pair of the foreign server names of all the open connections that are + previously made to the foreign servers and <literal>true</literal> or + <literal>false</literal> to show whether or not the connection is valid. + The foreign server connections can get invalidated due to alter statements + on foreign server or user mapping. If there are no open connections, then + <literal>NULL</literal> is returned. This function issues a warning in case + for any connection, the associated foreign server has been dropped and the + server name can not be fetched from the system catalogues. + </para> + + <para> + <function>postgres_fdw_disconnect</function> ( <parameter>servername</parameter> <type>text</type> ) + which takes foreign server name as input. When called in the local session, + it discards the unused open connection previously made to the foreign server + and returns <literal>true</literal>. If the open connection is still being + used in the current transaction, it is not discarded, instead a warning is + issued and <literal>false</literal> is returned. <literal>false</literal> is + returned when there are no open connections. When there are some open + connections, but there is no connection for the given foreign server, + then <literal>false</literal> is returned. When no foreign server exists + with the given name, an error is emitted. + </para> + + <para> + <function>postgres_fdw_disconnect</function> ( ) which takes no input. + When called in the local session, it discards all the unused open + connections that are previously made to the foreign servers and returns + <literal>true</literal>. If there is any open connection that is still being + used in the current transaction, then a warning is issued. <literal>false</literal> + is returned when no open connection is discarded or there are no open + connections at all. + </para> + +</sect2> <sect2> <title>Connection Management</title> @@ -490,6 +530,21 @@ OPTIONS (ADD password_required 'false'); multiple user identities (user mappings) are used to access the foreign server, a connection is established for each user mapping. </para> + + <para> + Since the <filename>postgres_fdw</filename> keeps the connections to remote + servers in the local session, the corresponding sessions that are opened on + the remote servers are kept idle until they are re-used by the local session. + This may waste resources if those connections are not frequently used by the + local session. To address this, the <filename>postgres_fdw</filename> + provides following way to remove the connections to the remote servers and + so the remote sessions: + + <function>postgres_fdw_disconnect()</function> to discard all the + connections or <function>postgres_fdw_disconnect(text)</function> + to discard the connection associated with the given foreign server. + + </para> </sect2> <sect2> -- 2.25.1
From 13eccc4c4c4b2ac4548608f37b3518160e8f3283 Mon Sep 17 00:00:00 2001 From: Bharath Rupireddy <bharath.rupireddy@enterprisedb.com> Date: Fri, 1 Jan 2021 14:33:41 +0530 Subject: [PATCH v5 2/3] postgres_fdw add keep_connections GUC to not cache connections This patch adds a new GUC postgres_fdw.keep_connections, default being on, when set to off no remote connections are cached by the local session. --- contrib/postgres_fdw/connection.c | 12 +++-- .../postgres_fdw/expected/postgres_fdw.out | 50 +++++++++++++++++++ contrib/postgres_fdw/postgres_fdw.c | 16 ++++++ contrib/postgres_fdw/postgres_fdw.h | 3 ++ contrib/postgres_fdw/sql/postgres_fdw.sql | 32 +++++++++++- doc/src/sgml/postgres-fdw.sgml | 46 ++++++++++++++++- 6 files changed, 154 insertions(+), 5 deletions(-) diff --git a/contrib/postgres_fdw/connection.c b/contrib/postgres_fdw/connection.c index b9f6050f4b..323242c1d6 100644 --- a/contrib/postgres_fdw/connection.c +++ b/contrib/postgres_fdw/connection.c @@ -816,6 +816,7 @@ pgfdw_xact_callback(XactEvent event, void *arg) while ((entry = (ConnCacheEntry *) hash_seq_search(&scan))) { PGresult *res; + bool used_in_current_xact = false; /* Ignore cache entry if no open connection right now */ if (entry->conn == NULL) @@ -826,6 +827,8 @@ pgfdw_xact_callback(XactEvent event, void *arg) { bool abort_cleanup_failure = false; + used_in_current_xact = true; + elog(DEBUG3, "closing remote transaction on connection %p", entry->conn); @@ -960,16 +963,19 @@ pgfdw_xact_callback(XactEvent event, void *arg) /* * If the connection isn't in a good idle state or it is marked as - * invalid, then discard it to recover. Next GetConnection will open a - * new connection. + * invalid or keep_connections GUC is false and this connection is used + * in current xact, then discard it to recover. Next GetConnection will + * open a new connection. */ if (PQstatus(entry->conn) != CONNECTION_OK || PQtransactionStatus(entry->conn) != PQTRANS_IDLE || entry->changing_xact_state || - entry->invalidated) + entry->invalidated || + (used_in_current_xact && !keep_connections)) { elog(DEBUG3, "discarding connection %p", entry->conn); disconnect_pg_server(entry); + used_in_current_xact = false; } } diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out index ba29bc6131..e08d9f38be 100644 --- a/contrib/postgres_fdw/expected/postgres_fdw.out +++ b/contrib/postgres_fdw/expected/postgres_fdw.out @@ -9448,5 +9448,55 @@ DETAIL: Such connections are discarded at the end of remote transaction. (0 rows) COMMIT; +-- =================================================================== +-- Test postgres_fdw.keep_connections GUC +-- =================================================================== +-- By default, keep_connections GUC is on i.e. local session caches all the +-- foreign server connections. +SHOW postgres_fdw.keep_connections; + postgres_fdw.keep_connections +------------------------------- + on +(1 row) + +-- Set it off i.e. the cached connections which are used after this setting are +-- disconnected at the end of respective xacts. +SET postgres_fdw.keep_connections TO off; +-- Make connection using loopback server, connection should not be cached as +-- the GUC is off. +SELECT 1 FROM ft1 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +-- Should output nothing. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +------------ +(0 rows) + +-- Set it on i.e. connections are cached. +SET postgres_fdw.keep_connections TO on; +SELECT 1 FROM ft1 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +-- Should output loopback. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +------------------ + (loopback, true) +(1 row) + +-- Discard loopback connection. +SELECT * FROM postgres_fdw_disconnect(); /* TRUE */ + postgres_fdw_disconnect +------------------------- + t +(1 row) + -- Clean up. DROP FUNCTION fdw_unnest; diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c index b6c72e1d1e..160f17972b 100644 --- a/contrib/postgres_fdw/postgres_fdw.c +++ b/contrib/postgres_fdw/postgres_fdw.c @@ -302,6 +302,8 @@ typedef struct List *already_used; /* expressions already dealt with */ } ec_member_foreign_arg; +bool keep_connections = true; + /* * SQL functions */ @@ -506,6 +508,20 @@ static void merge_fdw_options(PgFdwRelationInfo *fpinfo, const PgFdwRelationInfo *fpinfo_o, const PgFdwRelationInfo *fpinfo_i); +void +_PG_init(void) +{ + DefineCustomBoolVariable("postgres_fdw.keep_connections", + "Enables postgres_fdw connection caching.", + "When off postgres_fdw will close connections at the end of transaction.", + &keep_connections, + true, + PGC_USERSET, + 0, + NULL, + NULL, + NULL); +} /* * Foreign-data wrapper handler function: return a struct with pointers diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h index eef410db39..7f1bdb96d6 100644 --- a/contrib/postgres_fdw/postgres_fdw.h +++ b/contrib/postgres_fdw/postgres_fdw.h @@ -124,9 +124,12 @@ typedef struct PgFdwRelationInfo int relation_index; } PgFdwRelationInfo; +extern bool keep_connections; + /* in postgres_fdw.c */ extern int set_transmission_modes(void); extern void reset_transmission_modes(int nestlevel); +extern void _PG_init(void); /* in connection.c */ extern PGconn *GetConnection(UserMapping *user, bool will_prep_stmt); diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql index 2267aee630..b37aa569d6 100644 --- a/contrib/postgres_fdw/sql/postgres_fdw.sql +++ b/contrib/postgres_fdw/sql/postgres_fdw.sql @@ -2875,5 +2875,35 @@ DROP SERVER temploopback2 CASCADE; SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; /* WARNING */ COMMIT; +-- =================================================================== +-- Test postgres_fdw.keep_connections GUC +-- =================================================================== + +-- By default, keep_connections GUC is on i.e. local session caches all the +-- foreign server connections. +SHOW postgres_fdw.keep_connections; + +-- Set it off i.e. the cached connections which are used after this setting are +-- disconnected at the end of respective xacts. +SET postgres_fdw.keep_connections TO off; + +-- Make connection using loopback server, connection should not be cached as +-- the GUC is off. +SELECT 1 FROM ft1 LIMIT 1; + +-- Should output nothing. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + +-- Set it on i.e. connections are cached. +SET postgres_fdw.keep_connections TO on; + +SELECT 1 FROM ft1 LIMIT 1; + +-- Should output loopback. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + +-- Discard loopback connection. +SELECT * FROM postgres_fdw_disconnect(); /* TRUE */ + -- Clean up. -DROP FUNCTION fdw_unnest; +DROP FUNCTION fdw_unnest; \ No newline at end of file diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml index 405923f2aa..15def846f5 100644 --- a/doc/src/sgml/postgres-fdw.sgml +++ b/doc/src/sgml/postgres-fdw.sgml @@ -519,6 +519,44 @@ OPTIONS (ADD password_required 'false'); </sect2> +<sect2> + <title>Configuration Parameters</title> + + <variablelist> + <varlistentry> + + <term> + <varname>postgres_fdw.keep_connections</varname> (<type>boolean</type>) + <indexterm> + <primary><varname>postgres_fdw.keep_connections</varname> configuration parameter</primary> + </indexterm> + </term> + + <listitem> + + <para> + Allows <filename>postgres_fdw</filename> to keep or discard the + connection made to the foreign server by the local session. Default is + <literal>on</literal>. When set to <literal>off</literal> the local + session doesn't keep the connections made to the foreign servers. Each + connection is discarded at the end of transaction in which it is used. + </para> + + <para> + Note that setting <varname>postgres_fdw.keep_connections</varname> to + <literal>off</literal> does not discard any previously made and still open + connections immediately. They will be closed only at the end of future + transactions, which operated on them. To close all connections + immediately use <function>postgres_fdw_disconnect</function> function. + </para> + + </listitem> + + </varlistentry> + </variablelist> + + </sect2> + <sect2> <title>Connection Management</title> @@ -537,12 +575,18 @@ OPTIONS (ADD password_required 'false'); the remote servers are kept idle until they are re-used by the local session. This may waste resources if those connections are not frequently used by the local session. To address this, the <filename>postgres_fdw</filename> - provides following way to remove the connections to the remote servers and + provides following ways to remove the connections to the remote servers and so the remote sessions: <function>postgres_fdw_disconnect()</function> to discard all the connections or <function>postgres_fdw_disconnect(text)</function> to discard the connection associated with the given foreign server. + + A configuration parameter, <varname>postgres_fdw.keep_connections</varname>, + default being <literal>on</literal>, when set to <literal>off</literal>, the + local session doesn't keep remote connections that are made to the foreign + servers. Each connection is discarded at the end of transaction in which it + is used. </para> </sect2> -- 2.25.1
From c0dff6ca64126a29ef1e395dbe8cc2176f465b68 Mon Sep 17 00:00:00 2001 From: Bharath Rupireddy <bharath.rupireddy@enterprisedb.com> Date: Fri, 1 Jan 2021 15:02:28 +0530 Subject: [PATCH v5 3/3] postgres_fdw server level option, keep_connection to not cache connection This patch adds a new server level option, keep_connection, default being on, when set to off, the local session doesn't cache the connections associated with the foreign server. --- contrib/postgres_fdw/connection.c | 35 ++++++++++++--- .../postgres_fdw/expected/postgres_fdw.out | 44 ++++++++++++++++++- contrib/postgres_fdw/option.c | 9 +++- contrib/postgres_fdw/sql/postgres_fdw.sql | 26 +++++++++++ doc/src/sgml/postgres-fdw.sgml | 42 ++++++++++++++++++ 5 files changed, 149 insertions(+), 7 deletions(-) diff --git a/contrib/postgres_fdw/connection.c b/contrib/postgres_fdw/connection.c index 323242c1d6..acb97d40cf 100644 --- a/contrib/postgres_fdw/connection.c +++ b/contrib/postgres_fdw/connection.c @@ -62,6 +62,8 @@ typedef struct ConnCacheEntry Oid serverid; uint32 server_hashvalue; /* hash value of foreign server OID */ uint32 mapping_hashvalue; /* hash value of user mapping OID */ + /* Keep or discard this connection at the end of xact */ + bool keep_connection; } ConnCacheEntry; /* @@ -124,6 +126,8 @@ GetConnection(UserMapping *user, bool will_prep_stmt) ConnCacheEntry *entry; ConnCacheKey key; MemoryContext ccxt = CurrentMemoryContext; + ListCell *lc; + ForeignServer *server; /* First time through, initialize connection cache hashtable */ if (ConnectionHash == NULL) @@ -261,6 +265,15 @@ GetConnection(UserMapping *user, bool will_prep_stmt) begin_remote_xact(entry); } + server = GetForeignServer(user->serverid); + foreach(lc, server->options) + { + DefElem *def = (DefElem *) lfirst(lc); + + if (strcmp(def->defname, "keep_connection") == 0) + entry->keep_connection = defGetBoolean(def); + } + /* Remember if caller will prepare statements */ entry->have_prep_stmt |= will_prep_stmt; @@ -285,6 +298,7 @@ make_new_connection(ConnCacheEntry *entry, UserMapping *user) entry->changing_xact_state = false; entry->invalidated = false; entry->serverid = server->serverid; + entry->keep_connection = true; entry->server_hashvalue = GetSysCacheHashValue1(FOREIGNSERVEROID, ObjectIdGetDatum(server->serverid)); @@ -963,15 +977,18 @@ pgfdw_xact_callback(XactEvent event, void *arg) /* * If the connection isn't in a good idle state or it is marked as - * invalid or keep_connections GUC is false and this connection is used - * in current xact, then discard it to recover. Next GetConnection will - * open a new connection. + * invalid or this connection is used in current xact and + * keep_connections GUC is false or GUC is true but the server level + * option is false, then discard it to recover. Next GetConnection will + * open a new connection. Note that keep_connections GUC overrides the + * server level keep_connection option. */ if (PQstatus(entry->conn) != CONNECTION_OK || PQtransactionStatus(entry->conn) != PQTRANS_IDLE || entry->changing_xact_state || entry->invalidated || - (used_in_current_xact && !keep_connections)) + (used_in_current_xact && + (!keep_connections || !entry->keep_connection))) { elog(DEBUG3, "discarding connection %p", entry->conn); disconnect_pg_server(entry); @@ -1132,7 +1149,15 @@ pgfdw_inval_callback(Datum arg, int cacheid, uint32 hashvalue) if (!ConnectionHash) return; - /* ConnectionHash must exist already, if we're registered */ + /* + * Since we can discard ConnectionHash with postgres_fdw_disconnect, we may + * have a NULL ConnectionHash. So return in that case. We do not need to + * invalidate the cache entries as the cache itself would have discarded + * with postgres_fdw_disconnect. + */ + if (!ConnectionHash) + return; + hash_seq_init(&scan, ConnectionHash); while ((entry = (ConnCacheEntry *) hash_seq_search(&scan))) { diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out index e08d9f38be..100a342c8b 100644 --- a/contrib/postgres_fdw/expected/postgres_fdw.out +++ b/contrib/postgres_fdw/expected/postgres_fdw.out @@ -8933,7 +8933,7 @@ DO $d$ END; $d$; ERROR: invalid option "password" -HINT: Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, requirepeer, ssl_min_protocol_version, ssl_max_protocol_version, gssencmode, krbsrvname, gsslib, target_session_attrs, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size +HINT: Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, requirepeer, ssl_min_protocol_version, ssl_max_protocol_version, gssencmode, krbsrvname, gsslib, target_session_attrs, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size, keep_connection CONTEXT: SQL statement "ALTER SERVER loopback_nopw OPTIONS (ADD password 'dummypw')" PL/pgSQL function inline_code_block line 3 at EXECUTE -- If we add a password for our user mapping instead, we should get a different @@ -9498,5 +9498,47 @@ SELECT * FROM postgres_fdw_disconnect(); /* TRUE */ t (1 row) +-- =================================================================== +-- Test foreign server level option keep_connection +-- =================================================================== +-- By default, the connections associated with foreign server are cached i.e. +-- keep_connection option is on. Set it to off. +ALTER SERVER loopback OPTIONS (keep_connection 'off'); +-- loopback server connection is closed by the local session at the end of xact +-- as the keep_connection was set to off. +SELECT 1 FROM ft1 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +-- Should output nothing. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +------------ +(0 rows) + +ALTER SERVER loopback OPTIONS (SET keep_connection 'on'); +-- loopback server connection should get cached. +SELECT 1 FROM ft1 LIMIT 1; + ?column? +---------- + 1 +(1 row) + +-- Should output loopback. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + fdw_unnest +------------------ + (loopback, true) +(1 row) + +-- Discard loopback connection. +SELECT * FROM postgres_fdw_disconnect(); /* TRUE */ + postgres_fdw_disconnect +------------------------- + t +(1 row) + -- Clean up. DROP FUNCTION fdw_unnest; diff --git a/contrib/postgres_fdw/option.c b/contrib/postgres_fdw/option.c index 1a03e02263..0fe2eff878 100644 --- a/contrib/postgres_fdw/option.c +++ b/contrib/postgres_fdw/option.c @@ -107,7 +107,8 @@ postgres_fdw_validator(PG_FUNCTION_ARGS) * Validate option value, when we can do so without any context. */ if (strcmp(def->defname, "use_remote_estimate") == 0 || - strcmp(def->defname, "updatable") == 0) + strcmp(def->defname, "updatable") == 0 || + strcmp(def->defname, "keep_connection") == 0) { /* these accept only boolean values */ (void) defGetBoolean(def); @@ -213,6 +214,12 @@ InitPgFdwOptions(void) {"sslcert", UserMappingRelationId, true}, {"sslkey", UserMappingRelationId, true}, + /* + * If true, cache the connection associated with this server, otherwise + * remove it at the end of the xact. Default is true. + */ + {"keep_connection", ForeignServerRelationId, false}, + {NULL, InvalidOid, false} }; diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql index b37aa569d6..44e076b4f4 100644 --- a/contrib/postgres_fdw/sql/postgres_fdw.sql +++ b/contrib/postgres_fdw/sql/postgres_fdw.sql @@ -2905,5 +2905,31 @@ SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; -- Discard loopback connection. SELECT * FROM postgres_fdw_disconnect(); /* TRUE */ +-- =================================================================== +-- Test foreign server level option keep_connection +-- =================================================================== + +-- By default, the connections associated with foreign server are cached i.e. +-- keep_connection option is on. Set it to off. +ALTER SERVER loopback OPTIONS (keep_connection 'off'); + +-- loopback server connection is closed by the local session at the end of xact +-- as the keep_connection was set to off. +SELECT 1 FROM ft1 LIMIT 1; + +-- Should output nothing. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + +ALTER SERVER loopback OPTIONS (SET keep_connection 'on'); + +-- loopback server connection should get cached. +SELECT 1 FROM ft1 LIMIT 1; + +-- Should output loopback. +SELECT * FROM fdw_unnest(postgres_fdw_get_connections()) ORDER BY 1; + +-- Discard loopback connection. +SELECT * FROM postgres_fdw_disconnect(); /* TRUE */ + -- Clean up. DROP FUNCTION fdw_unnest; \ No newline at end of file diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml index 15def846f5..a62460704f 100644 --- a/doc/src/sgml/postgres-fdw.sgml +++ b/doc/src/sgml/postgres-fdw.sgml @@ -478,6 +478,35 @@ OPTIONS (ADD password_required 'false'); </sect3> + <sect3> + <title>Connection Management Options</title> + + <para> + By default the foreign server connections made with + <filename>postgres_fdw</filename> are kept in local session for re-use. + This may be overridden using the following + <xref linkend="sql-createserver"/> option: + </para> + + <variablelist> + + <varlistentry> + <term><literal>keep_connection</literal></term> + <listitem> + <para> + This option controls whether <filename>postgres_fdw</filename> keeps the + server connection that is made with a specific foreign server. It can be + specified for a foreign server. Default is <literal>on</literal>. When + set to <literal>off</literal>, the associated foreign server connection + is discarded at the end of the transaction. + </para> + + </listitem> + </varlistentry> + + </variablelist> + </sect3> + <sect2> <title>Functions</title> @@ -542,6 +571,14 @@ OPTIONS (ADD password_required 'false'); connection is discarded at the end of transaction in which it is used. </para> + <para> + <varname>postgres_fdw.keep_connections</varname> configuration parameter + overrides the server level <literal>keep_connection</literal> option. + Which means that when the configuration parameter is set to + <literal>on</literal>, irrespective of the server option + <literal>keep_connection</literal> setting, the connections are discarded. + </para> + <para> Note that setting <varname>postgres_fdw.keep_connections</varname> to <literal>off</literal> does not discard any previously made and still open @@ -588,6 +625,11 @@ OPTIONS (ADD password_required 'false'); servers. Each connection is discarded at the end of transaction in which it is used. + A server level option, <literal>keep_connection</literal> that is used with + <xref linkend="sql-createserver"/>. Default being <literal>on</literal>, + when set to <literal>off</literal> the local session doesn't keep remote + connection associated with the foreign server. The connection is + discarded at the end of the transaction. </para> </sect2> -- 2.25.1