Re: POC: postgres_fdw insert batching

On Fri, Jan 15, 2021 at 12:05 AM Tomas Vondra
<tomas(dot)vondra(at)enterprisedb(dot)com> wrote:
> Attached is v9 with all of those tweaks,

Thanks.

> except for moving the BatchSize
> call to BeginForeignModify - I tried that, but it did not seem like an
> improvement, because we'd still need the checks for API callbacks in
> ExecInsert for example. So I decided not to do that.

Okay, so maybe not moving the whole logic into the FDW's
BeginForeignModify(), but at least if we move this...

@@ -441,6 +449,72 @@ ExecInsert(ModifyTableState *mtstate,
+ /*
+ * Determine if the FDW supports batch insert and determine the batch
+ * size (a FDW may support batching, but it may be disabled for the
+ * server/table). Do this only once, at the beginning - we don't want
+ * the batch size to change during execution.
+ */
+ if (resultRelInfo->ri_FdwRoutine->GetForeignModifyBatchSize &&
+ resultRelInfo->ri_FdwRoutine->ExecForeignBatchInsert &&
+ resultRelInfo->ri_BatchSize == 0)
+ resultRelInfo->ri_BatchSize =
+
resultRelInfo->ri_FdwRoutine->GetForeignModifyBatchSize(resultRelInfo);

...into ExecInitModifyTable(), ExecInsert() only needs the following block:

/*
+ * If the FDW supports batching, and batching is requested, accumulate
+ * rows and insert them in batches. Otherwise use the per-row inserts.
+ */
+ if (resultRelInfo->ri_BatchSize > 1)
+ {
+ ...

AFAICS, I don't see anything that will cause ri_BatchSize to become 0
once set so don't see the point of checking whether it needs to be set
again on every ExecInsert() call. Also, maybe not that important, but
shaving off 3 comparisons for every tuple would add up nicely IMHO
especially given that we're targeting bulk loads.

--
Amit Langote
EDB: http://www.enterprisedb.com