Hi, I took at this patch today. I did some minor changes, mostly:
1) change the code limiting batch_size from if (fmstate->p_nums > 0 && (batch_size * fmstate->p_nums > PQ_QUERY_PARAM_MAX_LIMIT)) { batch_size = PQ_QUERY_PARAM_MAX_LIMIT / fmstate->p_nums; } to if (fmstate && fmstate->p_nums > 0) batch_size = Min(batch_size, PQ_QUERY_PARAM_MAX_LIMIT / fmstate->p_nums); which I think is somewhat clearer / more common patter. 2) I've reworded the docs a bit, splitting the single para into two. I think this makes it clearer. Attached is a patch doing this. Please check the commit message etc. Barring objections I'll get it committed in a couple days. regards -- Tomas Vondra EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
>From 222806c4eef0fb3a021da3c1d4cc9e1e41bd9ddf Mon Sep 17 00:00:00 2001 From: Tomas Vondra <to...@2ndquadrant.com> Date: Sun, 30 May 2021 20:58:38 +0200 Subject: [PATCH] Make sure postgres_fdw batching does 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 <houzj.f...@cn.fujitsu.com> Reviewed-by: Bharath Rupireddy <bharath.rupireddyforpostg...@gmail.com> Discussion: https://postgr.es/m/OS0PR01MB571603973C0AC2874AD6BF2594299%40OS0PR01MB5716.jpnprd01.prod.outlook.com --- contrib/postgres_fdw/postgres_fdw.c | 11 +++++++++-- doc/src/sgml/postgres-fdw.sgml | 11 +++++++++++ src/interfaces/libpq/fe-exec.c | 21 ++++++++++++--------- src/interfaces/libpq/libpq-fe.h | 2 ++ 4 files changed, 34 insertions(+), 11 deletions(-) diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c index c48a421e88..ac86b06b8f 100644 --- a/contrib/postgres_fdw/postgres_fdw.c +++ b/contrib/postgres_fdw/postgres_fdw.c @@ -1979,7 +1979,7 @@ 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. */ @@ -1994,7 +1994,14 @@ 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 64k (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/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml index fb87372bde..564651dfaa 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 <literal>1</literal>. </para> + + <para> + Note the actual number of rows <filename>postgres_fdw</filename> inserts at + once depends on the number of columns and the provided + <literal>batch_size</literal> value. The batch is executed as a single + query, and the libpq protocol (which <filename>postgres_fdw</filename> + uses to connect to a remote server) limits the number of parameters in a + single query to 64k. When the number of columns * <literal>batch_size</literal> + exceeds the limit, the <literal>batch_size</literal> will be adjusted to + avoid an error. + </para> </listitem> </varlistentry> diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c index 03592bdce9..832d61c544 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 227adde5a5..113ab52ada 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, -- 2.31.1