From 2da884f1dab6278a1a3fd71faf02f659da71934f Mon Sep 17 00:00:00 2001 From: Hayato Kuroda Date: Fri, 27 Jan 2023 03:17:30 +0000 Subject: [PATCH v34 2/3] postgres_fdw: add postgres_fdw_verify_connection_states This function can verify the status of connections that are establieshed by postgres_fdw. This check wil be done by PQconnCheck(), which means this is available only on systems that support the non-standard POLLRDHUP extension to the poll system call, including Linux. This returns true if existing connection is not closed by the remote peer. --- contrib/postgres_fdw/Makefile | 2 +- contrib/postgres_fdw/connection.c | 162 ++++++++++++++++++ contrib/postgres_fdw/meson.build | 1 + .../postgres_fdw/postgres_fdw--1.1--1.2.sql | 19 ++ contrib/postgres_fdw/postgres_fdw.control | 2 +- doc/src/sgml/postgres-fdw.sgml | 74 ++++++++ 6 files changed, 258 insertions(+), 2 deletions(-) create mode 100644 contrib/postgres_fdw/postgres_fdw--1.1--1.2.sql diff --git a/contrib/postgres_fdw/Makefile b/contrib/postgres_fdw/Makefile index c1b0cad453..6d23768389 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 postgres_fdw--1.0--1.1.sql +DATA = postgres_fdw--1.0.sql postgres_fdw--1.0--1.1.sql postgres_fdw--1.1--1.2.sql REGRESS = postgres_fdw diff --git a/contrib/postgres_fdw/connection.c b/contrib/postgres_fdw/connection.c index 12b54f15cd..99aff6304e 100644 --- a/contrib/postgres_fdw/connection.c +++ b/contrib/postgres_fdw/connection.c @@ -87,6 +87,9 @@ static bool xact_got_connection = false; PG_FUNCTION_INFO_V1(postgres_fdw_get_connections); PG_FUNCTION_INFO_V1(postgres_fdw_disconnect); PG_FUNCTION_INFO_V1(postgres_fdw_disconnect_all); +PG_FUNCTION_INFO_V1(postgres_fdw_verify_connection_states); +PG_FUNCTION_INFO_V1(postgres_fdw_verify_connection_states_all); +PG_FUNCTION_INFO_V1(postgres_fdw_can_verify_connection_states); /* prototypes of private functions */ static void make_new_connection(ConnCacheEntry *entry, UserMapping *user); @@ -117,6 +120,7 @@ static void pgfdw_finish_pre_subcommit_cleanup(List *pending_entries, int curlevel); static bool UserMappingPasswordRequired(UserMapping *user); static bool disconnect_cached_connections(Oid serverid); +static bool verify_cached_connections(Oid serverid, bool *checked); /* * Get a PGconn which can be used to execute queries on the remote PostgreSQL @@ -1832,3 +1836,161 @@ disconnect_cached_connections(Oid serverid) return result; } + +/* + * Workhorse to verify cached connections. + * + * This function scans all the connection cache entries and verifies the + * connections whose foreign server OID matches with the specified one. If + * InvalidOid is specified, it verifies all the cached connections. + * + * This function emits warnings if a disconnection is found. This return true + * if disconnections cannot be found, otherwise return false. + * + * checked will be set to true if PQconnCheck() is called at least once. + */ +static bool +verify_cached_connections(Oid serverid, bool *checked) +{ + HASH_SEQ_STATUS scan; + ConnCacheEntry *entry; + bool all = !OidIsValid(serverid); + bool result = true; + StringInfoData str; + + *checked = false; + + Assert(ConnectionHash); + + hash_seq_init(&scan, ConnectionHash); + while ((entry = (ConnCacheEntry *) hash_seq_search(&scan))) + { + /* Ignore cache entry if no open connection right now */ + if (!entry->conn) + continue; + + /* Skip if the entry is invalidated */ + if (entry->invalidated) + continue; + + if (all || entry->serverid == serverid) + { + if (PQconnCheck(entry->conn)) + { + /* A foreign server might be down, so construct a message */ + ForeignServer *server = GetForeignServer(entry->serverid); + + if (result) + { + /* + * Initialize and add a prefix if this is the first + * disconnection we found. + */ + initStringInfo(&str); + appendStringInfo(&str, "could not connect to server "); + + result = false; + } + else + appendStringInfo(&str, ", "); + + appendStringInfo(&str, "\"%s\"", server->servername); + } + + /* Set a flag to notify the caller */ + *checked = true; + } + } + + /* Raise a warning if disconnections are found */ + if (!result) + { + Assert(str.len); + ereport(WARNING, + (errcode(ERRCODE_CONNECTION_FAILURE), + errmsg("%s", str.data), + errdetail("Connection close is detected."), + errhint("Plsease check the health of server."))); + pfree(str.data); + } + + return result; +} + +/* + * Verify the specified cached connections. + * + * This function verifies the connections that are established by postgres_fdw + * from the local session to the foreign server with the given name. + * + * This function emits a warning if a disconnection is found. This returns true + * if existing connection is not closed by the remote peer. false is returned + * if the local session seems to be disconnected from other servers. NULL is + * returned if a connection to the specified foreign server has not been + * established yet, or this function is not available on this platform. + */ +Datum +postgres_fdw_verify_connection_states(PG_FUNCTION_ARGS) +{ + ForeignServer *server; + char *servername; + bool result, + checked = false; + + /* quick exit if the checking does not work well on this platfrom */ + if (!PQconnCheckable()) + PG_RETURN_NULL(); + + /* quick exit if connection cache has not been initialized yet */ + if (!ConnectionHash) + PG_RETURN_NULL(); + + servername = text_to_cstring(PG_GETARG_TEXT_PP(0)); + server = GetForeignServerByName(servername, false); + + result = verify_cached_connections(server->serverid, &checked); + + /* Return the result if checking function was called, otherwise NULL */ + if (checked) + PG_RETURN_BOOL(result); + else + PG_RETURN_NULL(); +} + +/* + * Verify all the cached connections. + * + * This function verifies all the connections that are established by postgres_fdw + * from the local session to the foreign servers. + */ +Datum +postgres_fdw_verify_connection_states_all(PG_FUNCTION_ARGS) +{ + bool result, + checked = false; + + /* quick exit if the checking does not work well on this platfrom */ + if (!PQconnCheckable()) + PG_RETURN_NULL(); + + /* quick exit if connection cache has not been initialized yet */ + if (!ConnectionHash) + PG_RETURN_NULL(); + + result = verify_cached_connections(InvalidOid, &checked); + + /* Return the result if checking function was called, otherwise NULL */ + if (checked) + PG_RETURN_BOOL(result); + else + PG_RETURN_NULL(); +} + +/* + * Check whether functions for verifying cached connections work well or not + */ +Datum +postgres_fdw_can_verify_connection_states(PG_FUNCTION_ARGS) +{ + PG_RETURN_BOOL(PQconnCheckable()); +} diff --git a/contrib/postgres_fdw/meson.build b/contrib/postgres_fdw/meson.build index 2b451f165e..29118d47bb 100644 --- a/contrib/postgres_fdw/meson.build +++ b/contrib/postgres_fdw/meson.build @@ -26,6 +26,7 @@ install_data( 'postgres_fdw.control', 'postgres_fdw--1.0.sql', 'postgres_fdw--1.0--1.1.sql', + 'postgres_fdw--1.1--1.2.sql', kwargs: contrib_data_args, ) diff --git a/contrib/postgres_fdw/postgres_fdw--1.1--1.2.sql b/contrib/postgres_fdw/postgres_fdw--1.1--1.2.sql new file mode 100644 index 0000000000..a8556b4c9f --- /dev/null +++ b/contrib/postgres_fdw/postgres_fdw--1.1--1.2.sql @@ -0,0 +1,19 @@ +/* contrib/postgres_fdw/postgres_fdw--1.1--1.2.sql */ + +-- complain if script is sourced in psql, rather than via ALTER EXTENSION +\echo Use "ALTER EXTENSION postgres_fdw UPDATE TO '1.2'" to load this file. \quit + +CREATE FUNCTION postgres_fdw_verify_connection_states (text) +RETURNS bool +AS 'MODULE_PATHNAME' +LANGUAGE C STRICT PARALLEL RESTRICTED; + +CREATE FUNCTION postgres_fdw_verify_connection_states_all () +RETURNS bool +AS 'MODULE_PATHNAME' +LANGUAGE C STRICT PARALLEL RESTRICTED; + +CREATE FUNCTION postgres_fdw_can_verify_connection_states () +RETURNS bool +AS 'MODULE_PATHNAME' +LANGUAGE C STRICT PARALLEL SAFE; diff --git a/contrib/postgres_fdw/postgres_fdw.control b/contrib/postgres_fdw/postgres_fdw.control index d489382064..a4b800be4f 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 = '1.1' +default_version = '1.2' module_pathname = '$libdir/postgres_fdw' relocatable = true diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml index 644f51835b..85e21f8904 100644 --- a/doc/src/sgml/postgres-fdw.sgml +++ b/doc/src/sgml/postgres-fdw.sgml @@ -826,6 +826,80 @@ postgres=# SELECT postgres_fdw_disconnect_all(); + + + postgres_fdw_verify_connection_states(server_name text) returns boolean + + + This function checks the status of remote connections established by + postgres_fdw from the local session to the foreign + server with the given name. This check is performed by polling the socket + and allows long-running transactions to be aborted sooner if the kernel + reports that the connection is closed. This function is currently + available only on systems that support the non-standard POLLRDHUP + extension to the poll system call, including Linux. This + returns true if existing connection is not closed by + the remote peer. false is returned if the local + session seems to be disconnected from other servers. NULL + is returned if a connection to the specified foreign server has not been + established yet, or this function is not available on this platform. + If no foreign server with the given name is found, an error is reported. + Example usage of the function: + +postgres=# SELECT postgres_fdw_verify_connection_states('loopback1'); + postgres_fdw_verify_connection_states +--------------------------------------- + t + + + + + + postgres_fdw_verify_connection_states_all() returns boolean + + + This function checks the status of all the remote connections established + by postgres_fdw from the local session to the + foreign servers. This check is performed by polling the socket and allows + long-running transactions to be aborted sooner if the kernel reports + that the connection is closed. This function is currently available only + on systems that support the non-standard POLLRDHUP + extension to the poll system call, including Linux. This + returns true if all connections are not closed by the + remote peer. false is returned if the local session + seems to be disconnected from at least one remote server. NULL + is returned if the local session does not have connection caches, or this + function is not available on this platform. Example usage of the + function: + +postgres=# SELECT postgres_fdw_verify_connection_states_all(); + postgres_fdw_verify_connection_states_all +------------------------------------------- + t + + + + + + + postgres_fdw_can_verify_connection_states() returns boolean + + + This function checks whether postgres_fdw_verify_connection_states + and postgres_fdw_verify_connection_states work well + or not. This returns true if it can be used, otherwise + returns false. Example usage of the function: + + +postgres=# SELECT postgres_fdw_can_verify_connection_states(); + postgres_fdw_can_verify_connection_states +------------------------------------------- + t + + + + + -- 2.27.0