Re: BitmapHeapScan streaming read user and prelim refactoring

On 3/23/24 01:26, Melanie Plageman wrote:
> On Fri, Mar 22, 2024 at 08:22:11PM -0400, Melanie Plageman wrote:
>> On Tue, Mar 19, 2024 at 02:33:35PM +0200, Heikki Linnakangas wrote:
>>> On 18/03/2024 17:19, Melanie Plageman wrote:
>>>> I've attached v7 rebased over this commit.
>>>
>>> If we delayed table_beginscan_bm() call further, after starting the TBM
>>> iterator, we could skip it altogether when the iterator is empty.
>>>
>>> That's a further improvement, doesn't need to be part of this patch set.
>>> Just caught my eye while reading this.
>>
>> Hmm. You mean like until after the first call to tbm_[shared]_iterate()?
>> AFAICT, tbm_begin_iterate() doesn't tell us anything about whether or
>> not the iterator is "empty". Do you mean cases when the bitmap has no
>> blocks in it? It seems like we should be able to tell that from the
>> TIDBitmap.
>>
>>>
>>>> v7-0003-Push-BitmapHeapScan-skip-fetch-optimization-into-.patch
>>>
>>> I suggest to avoid the double negative with SO_CAN_SKIP_FETCH, and call the
>>> flag e.g. SO_NEED_TUPLE.
>>
>> Agreed. Done in attached v8. Though I wondered if it was a bit weird
>> that the flag is set in the common case and not set in the uncommon
>> case...
>
> v8 actually attached this time

I tried to run the benchmarks with v8, but unfortunately it crashes for
me very quickly (I've only seen 0015 to crash, so I guess the bug is in
that patch).

The backtrace attached, this doesn't seem right:

(gdb) p hscan->rs_cindex
$1 = 543516018

regards

--
Tomas Vondra
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