Horton

Re: Speed up Clog Access by increasing CLOG buffers

Dilip Kumar <dilipbalaut@gmail.com>

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From: Dilip Kumar <dilipbalaut@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Andres Freund <andres@anarazel.de>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2016-09-14T16:04:55Z
Lists: pgsql-hackers 
On Wed, Sep 14, 2016 at 8:59 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> Sure, but you're testing at *really* high client counts here.  Almost
> nobody is going to benefit from a 5% improvement at 256 clients.

I agree with your point, but here we need to consider one more thing,
that on head we are gaining ~30% with both the approaches.

So for comparing these two patches we can consider..

A.  Other workloads (one can be as below)
   -> Load on CLogControlLock at commit (exclusive mode) + Load on
CLogControlLock at Transaction status (shared mode).
   I think we can mix (savepoint + updates)

B. Simplicity of the patch (if both are performing almost equal in all
practical scenarios).

C. Bases on algorithm whichever seems winner.

I will try to test these patches with other workloads...

>  You
> need to test 64 clients and 32 clients and 16 clients and 8 clients
> and see what happens there.  Those cases are a lot more likely than
> these stratospheric client counts.

I tested with 64 clients as well..
1. On head we are gaining ~15% with both the patches.
2. But group lock vs granular lock is almost same.

-- 
Regards,
Dilip Kumar
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.