Re: [HACKERS] Re: [GSOC 17] Eliminate O(N^2) scaling fromrw-conflict tracking in serializable transactions

Thank you very much! I follow your advice and here is the result. 

SerializableXactHashLock 73
predicate_lock_manager 605
WALWriteLock 3
SerializableFinishedListLock 665

There are more than 90 events each time.  SerializableXactHashLock/SerializableFinishedListLock are both used in SSI. 
I think that's why PG is so slow in high contention environment.


> -----Original Messages-----
> From: "Robert Haas" <robertmhaas@gmail.com>
> Sent Time: 2017-06-08 01:30:58 (Thursday)
> To: "Mengxing Liu" <liu-mx15@mails.tsinghua.edu.cn>
> Cc: kgrittn <kgrittn@gmail.com>, "Alvaro Herrera" <alvherre@2ndquadrant.com>, "pgsql-hackers@postgresql.org"
<pgsql-hackers@postgresql.org>
> Subject: Re: [HACKERS] Re: [GSOC 17] Eliminate O(N^2) scaling from rw-conflict tracking in serializable transactions
> 
> On Tue, Jun 6, 2017 at 12:16 PM, Mengxing Liu
> <liu-mx15@mails.tsinghua.edu.cn> wrote:
> > I think disk I/O is not the bottleneck in our experiment, but the global lock is.
> 
> A handy way to figure this kind of thing out is to run a query like
> this repeatedly during the benchmark:
> 
> SELECT wait_event_type, wait_event FROM pg_stat_activity;
> 
> I often do this by using psql's \watch command, often \watch 0.5 to
> run it every half-second.  I save all the results collected during the
> benchmark using 'script' and then analyze them to see which wait
> events are most frequent.  If your theory is right, you ought to see
> that SerializableXactHashLock occurs as a wait event very frequently.
> 
> -- 
> Robert Haas
> EnterpriseDB: http://www.enterprisedb.com
> The Enterprise PostgreSQL Company
> 
> 
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--
Mengxing Liu