Re: brininsert optimization opportunity

On 12/11/23 16:41, Tomas Vondra wrote:
> On 12/11/23 16:00, Alexander Lakhin wrote:
>> Hello Tomas and Soumyadeep,
>>
>> 25.11.2023 23:06, Tomas Vondra wrote:
>>> I've done a bit more cleanup on the last version of the patch (renamed
>>> the fields to start with bis_ as agreed, rephrased the comments / docs /
>>> commit message a bit) and pushed.
>>
>> Please look at a query, which produces warnings similar to the ones
>> observed upthread:
>> CREATE TABLE t(a INT);
>> INSERT INTO t SELECT x FROM generate_series(1,10000) x;
>> CREATE INDEX idx ON t USING brin (a);
>> REINDEX index CONCURRENTLY idx;
>>
>> WARNING:  resource was not closed: [1863] (rel=base/16384/16389,
>> blockNum=1, flags=0x93800000, refcount=1 1)
>> WARNING:  resource was not closed: [1862] (rel=base/16384/16389,
>> blockNum=0, flags=0x93800000, refcount=1 1)
>>
>> The first bad commit for this anomaly is c1ec02be1.
>>
> 
> Thanks for the report. I haven't investigated what the issue is, but it
> seems we fail to release the buffers in some situations - I'd bet we
> fail to call the cleanup callback in some place, or something like that.
> I'll take a look tomorrow.
> 

Yeah, just as I expected this seems to be a case of failing to call the
index_insert_cleanup after doing some inserts - in this case the inserts
happen in table_index_validate_scan, but validate_index has no idea it
needs to do the cleanup.

The attached 0001 patch fixes this by adding the call to validate_index,
which seems like the proper place as it's where the indexInfo is
allocated and destroyed.

But this makes me think - are there any other places that might call
index_insert without then also doing the cleanup? I did grep for the
index_insert() calls, and it seems OK except for this one.

There's a call in toast_internals.c, but that seems OK because that only
deals with btree indexes (and those don't need any cleanup). The same
logic applies to unique_key_recheck(). The rest goes through
execIndexing.c, which should do the cleanup in ExecCloseIndices().

Note: We should probably call the cleanup even in the btree cases, even
if only to make it clear it needs to be called after index_insert().

I was thinking maybe we should have some explicit call to destroy the
IndexInfo, but that seems rather inconvenient - it'd force everyone to
carefully track lifetimes of the IndexInfo instead of just relying on
memory context reset/destruction. That seems quite error-prone.

I propose we do a much simpler thing instead - allow the cache may be
initialized / cleaned up repeatedly, and make sure it gets reset at
convenient place (typically after index_insert calls that don't go
through execIndexing). That'd mean the cleanup does not need to happen
very far from the index_insert(), which makes the reasoning much easier.
0002 does this.

But maybe there's a better way to ensure the cleanup gets called even
when not using execIndexing.


regards

-- 
Tomas Vondra
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