Re: Don't overwrite scan key in systable_beginscan()

On Mon, Aug 12, 2024 at 09:44:02AM +0200, Peter Eisentraut wrote:
> Second (or 0005), an alternative to palloc is to make the converted scan
> keys a normal local variable.  Then it's just a question of whether a
> smaller palloc is preferred over an over-allocated local variable.  I think
> I still prefer the palloc version, but it doesn't matter much either way I
> think.

Since 811af9786b, the palloc'd idxkey's seem to be leaking/accumulating
throughout the command.

I noticed this on the master branch while running ANALYZE on partitioned
table with 600 attributes, even though only 6 were being analyzed.

LOG:  level: 3; BuildRelationExtStatistics: 1239963512 total in 278 blocks; 5082984 free (296 chunks); 1234880528 used

Several indexes are being scanned many thousands of times.

 310690 beginscan 2659
 310689 beginscan 2662
  77672 beginscan 2678

postgres=# SELECT 2659::REGCLASS;
regclass | pg_attribute_relid_attnum_index

postgres=# SELECT 2662::REGCLASS;
regclass | pg_class_oid_index

postgres=# SELECT 2678::REGCLASS;
regclass | pg_index_indrelid_index

> From 2f84e4d21ce611a4e6f428f72a18518e22776400 Mon Sep 17 00:00:00 2001
> From: Peter Eisentraut <peter@eisentraut.org>
> Date: Thu, 8 Aug 2024 08:27:26 +0200
> Subject: [PATCH v2 1/5] Don't overwrite scan key in systable_beginscan()
...
> Fix that by making a copy of the scan keys passed by the caller and
> make the modifications there.
> 
> diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
> index de751e8e4a3..b5eba549d3e 100644
> --- a/src/backend/access/index/genam.c
> +++ b/src/backend/access/index/genam.c
> @@ -419,17 +419,22 @@ systable_beginscan(Relation heapRelation,
>      if (irel)
>      {
>          int            i;
> +        ScanKey        idxkey;
>  
> -        /* Change attribute numbers to be index column numbers. */
> +        idxkey = palloc_array(ScanKeyData, nkeys);
> +
> +        /* Convert attribute numbers to be index column numbers. */
>          for (i = 0; i < nkeys; i++)