From 6524f8c6f0db13c5dca0438bdda194ee5bedebbb Mon Sep 17 00:00:00 2001 From: Tomas Vondra Date: Fri, 18 Feb 2022 01:32:25 +0100 Subject: [PATCH 1/2] postgres_fdw: track server version for connections To allow using features that only exist on new Postgres versions, we need some information about version of the remote node. We simply request server_version_num from the remote node. We only fetch it if version number is actually needed, and we cache it. --- contrib/postgres_fdw/connection.c | 44 +++++++++++++++++++++++++++++ contrib/postgres_fdw/postgres_fdw.h | 2 ++ 2 files changed, 46 insertions(+) diff --git a/contrib/postgres_fdw/connection.c b/contrib/postgres_fdw/connection.c index f753c6e2324..3ea2948d3ec 100644 --- a/contrib/postgres_fdw/connection.c +++ b/contrib/postgres_fdw/connection.c @@ -279,6 +279,50 @@ GetConnection(UserMapping *user, bool will_prep_stmt, PgFdwConnState **state) return entry->conn; } +/* + * Determine remote server version (as an int value). + * + * The value is determined only once and then cached in PgFdwConnState. + */ +int +GetServerVersion(PGconn *conn, PgFdwConnState *state) +{ + PGresult *volatile res = NULL; + + /* + * If we already know server version for this connection, we're done. + */ + if (state->server_version_num != 0) + return state->server_version_num; + + /* PGresult must be released before leaving this function. */ + PG_TRY(); + { + char *line; + + /* + * Execute EXPLAIN remotely. + */ + res = pgfdw_exec_query(conn, "SHOW server_version_num", NULL); + if (PQresultStatus(res) != PGRES_TUPLES_OK) + pgfdw_report_error(ERROR, res, conn, false, "SHOW server_version_num"); + + /* + * Extract the server version number. + */ + line = PQgetvalue(res, 0, 0); + state->server_version_num = strtol(line, NULL, 10); + } + PG_FINALLY(); + { + if (res) + PQclear(res); + } + PG_END_TRY(); + + return state->server_version_num; +} + /* * Reset all transient state fields in the cached connection entry and * establish new connection to the remote server. diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h index 8ae79e97e44..1687c62df2d 100644 --- a/contrib/postgres_fdw/postgres_fdw.h +++ b/contrib/postgres_fdw/postgres_fdw.h @@ -132,6 +132,7 @@ typedef struct PgFdwRelationInfo typedef struct PgFdwConnState { AsyncRequest *pendingAreq; /* pending async request */ + int server_version_num; /* remote server version */ } PgFdwConnState; /* in postgres_fdw.c */ @@ -143,6 +144,7 @@ extern void process_pending_request(AsyncRequest *areq); extern PGconn *GetConnection(UserMapping *user, bool will_prep_stmt, PgFdwConnState **state); extern void ReleaseConnection(PGconn *conn); +extern int GetServerVersion(PGconn *conn, PgFdwConnState *state); extern unsigned int GetCursorNumber(PGconn *conn); extern unsigned int GetPrepStmtNumber(PGconn *conn); extern void do_sql_command(PGconn *conn, const char *sql); -- 2.34.1