Horton

Re: Speed up Clog Access by increasing CLOG buffers

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Jim Nasby <Jim.Nasby@bluetreble.com>, Dilip Kumar <dilipbalaut@gmail.com>, Andres Freund <andres@anarazel.de>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2016-12-23T02:58:46Z
Lists: pgsql-hackers 
On Thu, Dec 22, 2016 at 6:59 PM, Tomas Vondra
<tomas.vondra@2ndquadrant.com> wrote:
> Hi,
>
> But as discussed with Amit in Tokyo at pgconf.asia, I got access to a
> Power8e machine (IBM 8247-22L to be precise). It's a much smaller machine
> compared to the x86 one, though - it only has 24 cores in 2 sockets, 128GB
> of RAM and less powerful storage, for example.
>
> I've repeated a subset of x86 tests and pushed them to
>
>     https://bitbucket.org/tvondra/power8-results-2
>
> The new results are prefixed with "power-" and I've tried to put them right
> next to the "same" x86 tests.
>
> In all cases the patches significantly reduce the contention on
> CLogControlLock, just like on x86. Which is good and expected.
>

The results look positive.  Do you think we can conclude based on all
the tests you and Dilip have done, that we can move forward with this
patch (in particular group-update) or do you still want to do more
tests?   I am aware that in one of the tests we have observed that
reducing contention on CLOGControlLock has increased the contention on
WALWriteLock, but I feel we can leave that point as a note to
committer and let him take a final call.  From the code perspective
already Robert and Andres have taken one pass of review and I have
addressed all their comments, so surely more review of code can help,
but I think that is not a big deal considering patch size is
relatively small.


-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com

Commits

  1. Use group updates when setting transaction status in clog.

  2. Improve 64bit atomics support.

  3. Add ProcArrayGroupUpdate wait event.

  4. Make the different Unix-y semaphore implementations ABI-compatible.

  5. Fix broken ALTER INDEX documentation

  6. Code and docs review for commit 3187d6de0e5a9e805b27c48437897e8c39071d45.

  7. Partition the freelist for shared dynahash tables.

  8. Correct StartupSUBTRANS for page wraparound

  9. Make idle backends exit if the postmaster dies.

  10. contrib/sslinfo: add ssl_extension_info SRF

  11. Reduce ProcArrayLock contention by removing backends in batches.

  12. Fix `make installcheck` for serializable transactions.

  13. Lockless StrategyGetBuffer clock sweep hot path.

  14. Reduce sinval synchronization overhead.