Re: Handing off SLRU fsyncs to the checkpointer

On 2020-Aug-25, Jakub Wartak wrote:

> Turning on/off the defer SLRU patch and/or fsync doesn't seem to make
> any difference, so if anyone is curious the next sets of append-only
> bottlenecks is like below:
>
> 14.69% postgres postgres [.] hash_search_with_hash_value
> ---hash_search_with_hash_value
> |--9.80%--BufTableLookup
> | ReadBuffer_common
> | ReadBufferWithoutRelcache
> | XLogReadBufferExtended
> | XLogReadBufferForRedoExtended
> | |--7.76%--btree_xlog_insert
> | | btree_redo
> | | StartupXLOG
> | --1.63%--heap_xlog_insert
> --4.90%--smgropen
> |--2.86%--ReadBufferWithoutRelcache

Looking at an earlier report of this problem I was thinking whether it'd
make sense to replace SMgrRelationHash with a simplehash table; I have a
half-written patch for that, but I haven't completed that work.
However, in the older profile things were looking different, as
hash_search_with_hash_value was taking 35.25%, and smgropen was 33.74%
of it. BufTableLookup was also there but only 1.51%. So I'm not so
sure now that that'll pay off as clearly as I had hoped.

--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services