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: Simon Riggs <simon@2ndquadrant.com>, Jesper Pedersen <jesper.pedersen@redhat.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2015-12-16T18:31:05Z
Lists: pgsql-hackers 
On Sat, Dec 12, 2015 at 8:03 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:

>>  I think it might be
>> advantageous to have at least two groups because otherwise things
>> might slow down when some transactions are rolling over to a new page
>> while others are still in flight for the previous page.  Perhaps we
>> should try it both ways and benchmark.
>>
>
> Sure, I can do the benchmarks with both the patches, but before that
> if you can once check whether group_slots_update_clog_v3.patch is inline
> with what you have in mind then it will be helpful.

Benchmarking sounds good.  This looks broadly like what I was thinking
about, although I'm not very sure you've got all the details right.

Some random comments:

- TransactionGroupUpdateXidStatus could do just as well without
add_proc_to_group.  You could just say if (group_no >= NUM_GROUPS)
break; instead.  Also, I think you could combine the two if statements
inside the loop.  if (nextidx != INVALID_PGPROCNO &&
ProcGlobal->allProcs[nextidx].clogPage == proc->clogPage) break; or
something like that.

- memberXid and memberXidstatus are terrible names.  Member of what?
That's going to be clear as mud to the next person looking at the
definitiono f PGPROC.  And the capitalization of memberXidstatus isn't
even consistent.  Nor is nextupdateXidStatusElem.  Please do give some
thought to the names you pick for variables and structure members.

-- 
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.