diff options
| author | Tomas Vondra | 2021-06-08 18:22:18 +0000 |
|---|---|---|
| committer | Tomas Vondra | 2021-06-08 18:28:31 +0000 |
| commit | cb92703384e2bb3fa0a690e5dbb95ad333c2b44c (patch) | |
| tree | 644c14c6f86391b0ae60736b36330b0caa387864 /doc/src/sgml/postgres-fdw.sgml | |
| parent | d1f0aa7696917213485c03b076b573497a535076 (diff) | |
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 <houzj.fnst@cn.fujitsu.com>
Reviewed-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Discussion: https://postgr.es/m/OS0PR01MB571603973C0AC2874AD6BF2594299%40OS0PR01MB5716.jpnprd01.prod.outlook.com
Diffstat (limited to 'doc/src/sgml/postgres-fdw.sgml')
| -rw-r--r-- | doc/src/sgml/postgres-fdw.sgml | 11 |
1 files changed, 11 insertions, 0 deletions
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 <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 65535. 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> |