From 8444117409b1d4326f3f8014aa29069a4493fd1f Mon Sep 17 00:00:00 2001 From: Hari Babu Date: Fri, 22 Feb 2019 00:22:43 +1100 Subject: [PATCH 4/4] New prefer-read target_session_attrs type With this prefer-read option type, application can prefer connecting to a read-only server if available from the list of hosts, otherwise connect it to read-write server --- doc/src/sgml/libpq.sgml | 15 ++- src/interfaces/libpq/fe-connect.c | 126 ++++++++++++++++++++++---- src/interfaces/libpq/libpq-fe.h | 3 +- src/interfaces/libpq/libpq-int.h | 10 +- src/test/recovery/t/001_stream_rep.pl | 14 ++- 5 files changed, 143 insertions(+), 25 deletions(-) diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml index 5c29beef51..d4bddef6cf 100644 --- a/doc/src/sgml/libpq.sgml +++ b/doc/src/sgml/libpq.sgml @@ -1585,8 +1585,19 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname returns on, the connection will be closed. If multiple hosts were specified in the connection string, any remaining servers will be tried just as if the connection - attempt had failed. The default value of this parameter, - any, regards all connections as acceptable. + attempt had failed. + + + + If this parameter is set to prefer-read, connections + where SHOW transaction_read_only returns on + are preferred. If no such connections can be found, then a connection + that allows read-write transactions will be accepted. + + + + The default value of this parameter is any, + regards all connections as acceptable. diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c index 25a153f48c..6943674067 100644 --- a/src/interfaces/libpq/fe-connect.c +++ b/src/interfaces/libpq/fe-connect.c @@ -322,7 +322,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = { {"target_session_attrs", "PGTARGETSESSIONATTRS", DefaultTargetSessionAttrs, NULL, - "Target-Session-Attrs", "", 11, /* sizeof("read-write") = 11 */ + "Target-Session-Attrs", "", 12, /* sizeof("prefer-read") = 12 */ offsetof(struct pg_conn, target_session_attrs)}, /* Terminating entry --- MUST BE LAST */ @@ -1243,6 +1243,8 @@ connectOptions2(PGconn *conn) conn->requested_session_type = SESSION_TYPE_ANY; else if (strcmp(conn->target_session_attrs, "read-write") == 0) conn->requested_session_type = SESSION_TYPE_READ_WRITE; + else if (strcmp(conn->target_session_attrs, "prefer-read") == 0) + conn->requested_session_type = SESSION_TYPE_PREFER_READ; else { conn->status = CONNECTION_BAD; @@ -2137,13 +2139,31 @@ keep_going: /* We will come back to here until there is if (conn->whichhost + 1 >= conn->nconnhost) { - /* - * Oops, no more hosts. An appropriate error message is already - * set up, so just set the right status. - */ - goto error_return; + if (conn->read_write_host_index >= 0) + { + /* + * Getting here means, failed to connect to read-only servers + * and now try connect to read-write server again. + */ + conn->whichhost = conn->read_write_host_index; + + /* + * Reset the host index value to avoid recursion during the + * second connection attempt. + */ + conn->read_write_host_index = -2; + } + else + { + /* + * Oops, no more hosts. An appropriate error message is already + * set up, so just set the right status. + */ + goto error_return; + } } - conn->whichhost++; + else + conn->whichhost++; /* Drop any address info for previous host */ release_conn_addrinfo(conn); @@ -2347,6 +2367,7 @@ keep_going: /* We will come back to here until there is conn->try_next_addr = true; goto keep_going; } + appendPQExpBuffer(&conn->errorMessage, libpq_gettext("could not create socket: %s\n"), SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf))); @@ -3225,14 +3246,16 @@ keep_going: /* We will come back to here until there is case CONNECTION_CHECK_TARGET: { /* - * If a read-write connection is required, see if we have one. + * If a read-write or prefer-read connection is required, + * see if we have one. * * Servers before 7.4 lack the transaction_read_only GUC, but * by the same token they don't have any read-only mode, so we * may just skip the test in that case. */ if (conn->sversion >= 70400 && - conn->requested_session_type == SESSION_TYPE_READ_WRITE) + (conn->requested_session_type == SESSION_TYPE_READ_WRITE || + conn->requested_session_type == SESSION_TYPE_PREFER_READ)) { if (conn->sversion < 120000) { @@ -3253,15 +3276,23 @@ keep_going: /* We will come back to here until there is restoreErrorMessage(conn, &savedMessage); goto error_return; } + conn->status = CONNECTION_CHECK_WRITABLE; + restoreErrorMessage(conn, &savedMessage); return PGRES_POLLING_READING; } - else if (conn->transaction_read_only) + else if ((conn->transaction_read_only + && (conn->requested_session_type == SESSION_TYPE_READ_WRITE)) || + (!conn->transaction_read_only + && (conn->requested_session_type == SESSION_TYPE_PREFER_READ) + && (conn->read_write_host_index != -2))) { - /* Not writable; fail this connection. */ + /* Not a requested type; fail this connection. */ const char *displayed_host; const char *displayed_port; + const char *type = (conn->requested_session_type == SESSION_TYPE_PREFER_READ) ? + "read-only" : "writable"; /* Append error report to conn->errorMessage. */ if (conn->connhost[conn->whichhost].type == CHT_HOST_ADDRESS) @@ -3273,15 +3304,19 @@ keep_going: /* We will come back to here until there is displayed_port = DEF_PGPORT_STR; appendPQExpBuffer(&conn->errorMessage, - libpq_gettext("could not make a writable " + libpq_gettext("could not make a %s " "connection to server " "\"%s:%s\"\n"), - displayed_host, displayed_port); + type, displayed_host, displayed_port); /* Close connection politely. */ conn->status = CONNECTION_OK; sendTerminateConn(conn); + /* Record read-write host index */ + if (conn->read_write_host_index == -1) + conn->read_write_host_index = conn->whichhost; + /* * Try next host if any, but we don't want to consider * additional addresses for this host. @@ -3289,6 +3324,39 @@ keep_going: /* We will come back to here until there is conn->try_next_host = true; goto keep_going; } + else /* obtained the requested type, consume it */ + { + /* We can release the address list now. */ + release_conn_addrinfo(conn); + + /* We are open for business! */ + conn->status = CONNECTION_OK; + return PGRES_POLLING_OK; + } + } + + /* + * Requested type is prefer-read, then record this host index + * and try the other before considering it later + */ + if ((conn->target_session_attrs != NULL) && + (conn->requested_session_type == SESSION_TYPE_PREFER_READ) && + (conn->read_write_host_index != -2)) + { + /* Close connection politely. */ + conn->status = CONNECTION_OK; + sendTerminateConn(conn); + + /* Record read-write host index */ + if (conn->read_write_host_index == -1) + conn->read_write_host_index = conn->whichhost; + + /* + * Try next host if any, but we don't want to consider + * additional addresses for this host. + */ + conn->try_next_host = true; + goto keep_going; } /* We can release the address list now. */ @@ -3358,11 +3426,22 @@ keep_going: /* We will come back to here until there is char *val; val = PQgetvalue(res, 0, 0); - if (strncmp(val, "on", 2) == 0) + + /* + * Server is read-only and requested mode is read-write, ignore it. + * Server is read-write and requested mode is prefer-read, record + * it for the first time and try to consume in the next scan (it means + * no read-only server is found in the first scan). + */ + if (((strncmp(val, "on", 2) == 0) && + (conn->requested_session_type == SESSION_TYPE_READ_WRITE)) || + ((strncmp(val, "off", 3) == 0) && + (conn->requested_session_type == SESSION_TYPE_PREFER_READ) && + (conn->read_write_host_index != -2))) { - /* Not writable; fail this connection. */ - const char *displayed_host; - const char *displayed_port; + /* Not a requested type; fail this connection. */ + const char *type = (conn->requested_session_type == SESSION_TYPE_PREFER_READ) ? + "read-only" : "writable"; PQclear(res); restoreErrorMessage(conn, &savedMessage); @@ -3377,15 +3456,19 @@ keep_going: /* We will come back to here until there is displayed_port = DEF_PGPORT_STR; appendPQExpBuffer(&conn->errorMessage, - libpq_gettext("could not make a writable " + libpq_gettext("could not make a %s " "connection to server " "\"%s:%s\"\n"), - displayed_host, displayed_port); + type, displayed_host, displayed_port); /* Close connection politely. */ conn->status = CONNECTION_OK; sendTerminateConn(conn); + /* Record read-write host index */ + if (conn->read_write_host_index == -1) + conn->read_write_host_index = conn->whichhost; + /* * Try next host if any, but we don't want to consider * additional addresses for this host. @@ -3394,7 +3477,7 @@ keep_going: /* We will come back to here until there is goto keep_going; } - /* Session is read-write, so we're good. */ + /* Session is requested type, so we're good. */ PQclear(res); termPQExpBuffer(&savedMessage); @@ -3608,6 +3691,9 @@ makeEmptyPGconn(void) conn = NULL; } + /* Initial value */ + conn->read_write_host_index = -1; + return conn; } diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h index 15bb82a885..a7de100c3b 100644 --- a/src/interfaces/libpq/libpq-fe.h +++ b/src/interfaces/libpq/libpq-fe.h @@ -74,7 +74,8 @@ typedef enum typedef enum { SESSION_TYPE_ANY = 0, /* Any session (default) */ - SESSION_TYPE_READ_WRITE /* Read-write session */ + SESSION_TYPE_READ_WRITE, /* Read-write session */ + SESSION_TYPE_PREFER_READ /* Prefer read only session */ } TargetSessionAttrsType; typedef enum diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h index b0ac98b90d..1878598633 100644 --- a/src/interfaces/libpq/libpq-int.h +++ b/src/interfaces/libpq/libpq-int.h @@ -363,7 +363,7 @@ struct pg_conn char *krbsrvname; /* Kerberos service name */ #endif - /* Type of connection to make. Possible values: any, read-write. */ + /* Type of connection to make. Possible values: any, read-write, perfer-read. */ char *target_session_attrs; TargetSessionAttrsType requested_session_type; @@ -400,6 +400,14 @@ struct pg_conn pg_conn_host *connhost; /* details about each named host */ char *connip; /* IP address for current network connection */ + /* + * First read-write host index in the connection string. + * + * Initial value is -1, then the index of the first read-write + * host, -2 during the second attempt of connection to avoid recursion. + */ + int read_write_host_index; + /* Connection data */ pgsocket sock; /* FD for socket, PGINVALID_SOCKET if * unconnected */ diff --git a/src/test/recovery/t/001_stream_rep.pl b/src/test/recovery/t/001_stream_rep.pl index beb45551a2..0e398136a5 100644 --- a/src/test/recovery/t/001_stream_rep.pl +++ b/src/test/recovery/t/001_stream_rep.pl @@ -3,7 +3,7 @@ use strict; use warnings; use PostgresNode; use TestLib; -use Test::More tests => 26; +use Test::More tests => 29; # Initialize master node my $node_master = get_new_node('master'); @@ -117,6 +117,18 @@ test_target_session_attrs($node_master, $node_standby_1, $node_master, "any", test_target_session_attrs($node_standby_1, $node_master, $node_standby_1, "any", 0); +# Connect to standby1 in "prefer-read" mode with master,standby1 list. +test_target_session_attrs($node_master, $node_standby_1, $node_standby_1, "prefer-read", + 0); + +# Connect to standby1 in "prefer-read" mode with standby1,master list. +test_target_session_attrs($node_standby_1, $node_master, $node_standby_1, + "prefer-read", 0); + +# Connect to node_master in "prefer-read" mode with only master list. +test_target_session_attrs($node_master, $node_master, $node_master, + "prefer-read", 0); + note "switching to physical replication slot"; # Switch to using a physical replication slot. We can do this without a new -- 2.20.1.windows.1