Re: strange perf regression with data checksums

On 5/19/25 20:44, Peter Geoghegan wrote:
> On Mon, May 19, 2025 at 2:19 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
>> On Mon, May 19, 2025 at 2:01 PM Tomas Vondra <tomas(at)vondra(dot)me> wrote:
>>> The regular index scan however still have this issue, although it's not
>>> as visible as for IOS.
>>
>> We can do somewhat better with plain index scans than my initial v1
>> prototype, without any major difficulties. There's more low-hanging
>> fruit.
>>
>> We could also move the call to BufferGetLSNAtomic (that currently
>> takes place inside _bt_readpage) over to _bt_drop_lock_and_maybe_pin.
>> That way we'd only need to call BufferGetLSNAtomic for those leaf
>> pages that will actually need to have some index tuples returned to
>> the scan (through the btgettuple interface).
>
> Attached is v2, which does things this way. What do you think?
>
> v2 also manages to avoid calling BufferGetLSNAtomic during all bitmap
> index scans. You didn't complain about any regressions in bitmap index
> scans, but I see no reason to take any chances (it's easy to just not
> call BufferGetLSNAtomic there).
>

Same effect as v1 for IOS, with regular index scans I see this:

64 clients: 0.7M tps
96 clients: 1.5M tps

So very similar improvement as for IOS.

regards

--
Tomas Vondra