Horton

Re: Speed up Clog Access by increasing CLOG buffers

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Thom Brown <thom@linux.com>, Simon Riggs <simon@2ndquadrant.com>, Jesper Pedersen <jesper.pedersen@redhat.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2016-02-23T13:36:46Z
Lists: pgsql-hackers 
On Sun, Feb 21, 2016 at 7:45 PM, Amit Kapila <amit.kapila16@gmail.com>
wrote:

> I mean, my basic feeling is that I would not accept a 2-3% regression in
>> the single client case to get a 10% speedup in the case where we have 128
>> clients.
>>
>
> I understand your point.  I think to verify whether it is run-to-run
> variation or an actual regression, I will re-run these tests on single
> client multiple times and post the result.
>

Perhaps you could also try it on a couple of different machines (e.g.
MacBook Pro and a couple of different large servers).


>
>   A lot of people will not have 128 clients; quite a few will have a
>> single session, or just a few.  Sometimes just making the code more complex
>> can hurt performance in subtle ways, e.g. by making it fit into the L1
>> instruction cache less well.  If the numbers you have here are accurate,
>> I'd vote to reject the patch.
>>
> One point to note is that this patch along with first patch which I
> posted in this thread to increase clog buffers can make significant
> reduction in contention on CLogControlLock.  OTOH, I think introducing
> regression at single-client is also not a sane thing to do, so lets
> first try to find if there is actually any regression and if it is, can
> we mitigate it by writing code with somewhat fewer instructions or
> in a slightly different way and then we can decide whether it is good
> to reject the patch or not.  Does that sound reasonable to you?
>

Yes.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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.