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Adjust batch size in postgres_fdw to not use too many parameters

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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.fnst@cn.fujitsu.com>
Reviewed-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Discussion: https://postgr.es/m/OS0PR01MB571603973C0AC2874AD6BF2594299%40OS0PR01MB5716.jpnprd01.prod.outlook.com
This commit is contained in:
Tomas Vondra
2021-06-08 20:22:18 +02:00
parent d1f0aa7696
commit cb92703384
6 changed files with 52 additions and 11 deletions
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11
contrib/postgres_fdw/postgres_fdw.c
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@ -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;
}