From cb92703384e2bb3fa0a690e5dbb95ad333c2b44c Mon Sep 17 00:00:00 2001 From: Tomas Vondra Date: Tue, 8 Jun 2021 20:22:18 +0200 Subject: [PATCH] Adjust batch size in postgres_fdw to not use too many parameters The FE/BE protocol identifies parameters with an Int16 index, which limits the maximum number of parameters per query to 65535. With batching added to postges_fdw this limit is much easier to hit, as the whole batch is essentially a single query, making this error much easier to hit. The failures are a bit unpredictable, because it also depends on the number of columns in the query. So instead of just failing, this patch tweaks the batch_size to not exceed the maximum number of parameters. Reported-by: Hou Zhijie Reviewed-by: Bharath Rupireddy Discussion: https://postgr.es/m/OS0PR01MB571603973C0AC2874AD6BF2594299%40OS0PR01MB5716.jpnprd01.prod.outlook.com --- .../postgres_fdw/expected/postgres_fdw.out | 11 ++++++++++ contrib/postgres_fdw/postgres_fdw.c | 11 ++++++++-- contrib/postgres_fdw/sql/postgres_fdw.sql | 7 +++++++ doc/src/sgml/postgres-fdw.sgml | 11 ++++++++++ src/interfaces/libpq/fe-exec.c | 21 +++++++++++-------- src/interfaces/libpq/libpq-fe.h | 2 ++ 6 files changed, 52 insertions(+), 11 deletions(-) diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out index 7b7c0db16cf..1fb26639fcb 100644 --- a/contrib/postgres_fdw/expected/postgres_fdw.out +++ b/contrib/postgres_fdw/expected/postgres_fdw.out @@ -9680,6 +9680,17 @@ SELECT COUNT(*) FROM ftable; 34 (1 row) +TRUNCATE batch_table; +DROP FOREIGN TABLE ftable; +-- try if large batches exceed max number of bind parameters +CREATE FOREIGN TABLE ftable ( x int ) SERVER loopback OPTIONS ( table_name 'batch_table', batch_size '100000' ); +INSERT INTO ftable SELECT * FROM generate_series(1, 70000) i; +SELECT COUNT(*) FROM ftable; + count +------- + 70000 +(1 row) + TRUNCATE batch_table; DROP FOREIGN TABLE ftable; -- Disable batch insert diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c index 0843ed9dba2..fafbab6b024 100644 --- a/contrib/postgres_fdw/postgres_fdw.c +++ b/contrib/postgres_fdw/postgres_fdw.c @@ -2030,7 +2030,7 @@ postgresGetForeignModifyBatchSize(ResultRelInfo *resultRelInfo) Assert(fmstate == NULL || fmstate->aux_fmstate == NULL); /* - * In EXPLAIN without ANALYZE, ri_fdwstate is NULL, so we have to lookup + * In EXPLAIN without ANALYZE, ri_FdwState is NULL, so we have to lookup * the option directly in server/table options. Otherwise just use the * value we determined earlier. */ @@ -2045,7 +2045,14 @@ postgresGetForeignModifyBatchSize(ResultRelInfo *resultRelInfo) resultRelInfo->ri_TrigDesc->trig_insert_after_row)) return 1; - /* Otherwise use the batch size specified for server/table. */ + /* + * Otherwise use the batch size specified for server/table. The number of + * parameters in a batch is limited to 65535 (uint16), so make sure we + * don't exceed this limit by using the maximum batch_size possible. + */ + if (fmstate && fmstate->p_nums > 0) + batch_size = Min(batch_size, PQ_QUERY_PARAM_MAX_LIMIT / fmstate->p_nums); + return batch_size; } diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql index 191efbf7c24..8cb2148f1f6 100644 --- a/contrib/postgres_fdw/sql/postgres_fdw.sql +++ b/contrib/postgres_fdw/sql/postgres_fdw.sql @@ -3026,6 +3026,13 @@ SELECT COUNT(*) FROM ftable; TRUNCATE batch_table; DROP FOREIGN TABLE ftable; +-- try if large batches exceed max number of bind parameters +CREATE FOREIGN TABLE ftable ( x int ) SERVER loopback OPTIONS ( table_name 'batch_table', batch_size '100000' ); +INSERT INTO ftable SELECT * FROM generate_series(1, 70000) i; +SELECT COUNT(*) FROM ftable; +TRUNCATE batch_table; +DROP FOREIGN TABLE ftable; + -- Disable batch insert CREATE FOREIGN TABLE ftable ( x int ) SERVER loopback OPTIONS ( table_name 'batch_table', batch_size '1' ); EXPLAIN (VERBOSE, COSTS OFF) INSERT INTO ftable VALUES (1), (2); diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml index 5aced083e9e..d96c3d0f0cd 100644 --- a/doc/src/sgml/postgres-fdw.sgml +++ b/doc/src/sgml/postgres-fdw.sgml @@ -372,6 +372,17 @@ OPTIONS (ADD password_required 'false'); overrides an option specified for the server. The default is 1. + + + Note the actual number of rows postgres_fdw inserts at + once depends on the number of columns and the provided + batch_size value. The batch is executed as a single + query, and the libpq protocol (which postgres_fdw + uses to connect to a remote server) limits the number of parameters in a + single query to 65535. When the number of columns * batch_size + exceeds the limit, the batch_size will be adjusted to + avoid an error. + diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c index 03592bdce9f..832d61c544f 100644 --- a/src/interfaces/libpq/fe-exec.c +++ b/src/interfaces/libpq/fe-exec.c @@ -1403,10 +1403,11 @@ PQsendQueryParams(PGconn *conn, libpq_gettext("command string is a null pointer\n")); return 0; } - if (nParams < 0 || nParams > 65535) + if (nParams < 0 || nParams > PQ_QUERY_PARAM_MAX_LIMIT) { - appendPQExpBufferStr(&conn->errorMessage, - libpq_gettext("number of parameters must be between 0 and 65535\n")); + appendPQExpBuffer(&conn->errorMessage, + libpq_gettext("number of parameters must be between 0 and %d\n"), + PQ_QUERY_PARAM_MAX_LIMIT); return 0; } @@ -1451,10 +1452,11 @@ PQsendPrepare(PGconn *conn, libpq_gettext("command string is a null pointer\n")); return 0; } - if (nParams < 0 || nParams > 65535) + if (nParams < 0 || nParams > PQ_QUERY_PARAM_MAX_LIMIT) { - appendPQExpBufferStr(&conn->errorMessage, - libpq_gettext("number of parameters must be between 0 and 65535\n")); + appendPQExpBuffer(&conn->errorMessage, + libpq_gettext("number of parameters must be between 0 and %d\n"), + PQ_QUERY_PARAM_MAX_LIMIT); return 0; } @@ -1548,10 +1550,11 @@ PQsendQueryPrepared(PGconn *conn, libpq_gettext("statement name is a null pointer\n")); return 0; } - if (nParams < 0 || nParams > 65535) + if (nParams < 0 || nParams > PQ_QUERY_PARAM_MAX_LIMIT) { - appendPQExpBufferStr(&conn->errorMessage, - libpq_gettext("number of parameters must be between 0 and 65535\n")); + appendPQExpBuffer(&conn->errorMessage, + libpq_gettext("number of parameters must be between 0 and %d\n"), + PQ_QUERY_PARAM_MAX_LIMIT); return 0; } diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h index 845b4c04c9c..ca733a20048 100644 --- a/src/interfaces/libpq/libpq-fe.h +++ b/src/interfaces/libpq/libpq-fe.h @@ -429,6 +429,8 @@ extern PGresult *PQexecPrepared(PGconn *conn, int resultFormat); /* Interface for multiple-result or asynchronous queries */ +#define PQ_QUERY_PARAM_MAX_LIMIT 65535 + extern int PQsendQuery(PGconn *conn, const char *query); extern int PQsendQueryParams(PGconn *conn, const char *command,