Re: Handing off SLRU fsyncs to the checkpointer

Hi Alvaro, Thomas, hackers

>> 14.69% postgres postgres [.] hash_search_with_hash_value
>> ---hash_search_with_hash_value
>> |--9.80%--BufTableLookup
[..]
>> --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.

Yes, quite frankly my expectation was to see hash_search_with_hash_value()<-smgropen() outcome as 1st one, but in simplified redo-bench script it's not the case. The original scenario was much more complex with plenty of differences (in no particular order: TB-sized DB VS ~500GB RAM -> thousands of forks, multiple tables, huge btrees, multiple INSERTs wih plenty of data in VALUES() thrown as one commit, real primary->hot-standby replication [not closed DB in recovery], sorted not random UUIDs) - I'm going to try nail down these differences and maybe I manage to produce more realistic "pgbench reproducer" (this may take some time though).

-Jakub Wartak.