Horton

Re: refactoring relation extension and BufferAlloc(), faster COPY

Nasby, Jim <nasbyj@amazon.com>

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From: Jim Nasby <nasbyj@amazon.com>
To: Andres Freund <andres@anarazel.de>
Cc: <pgsql-hackers@postgresql.org>, Thomas Munro <thomas.munro@gmail.com>, Melanie Plageman <melanieplageman@gmail.com>, Yura Sokolov <y.sokolov@postgrespro.ru>, Robert Haas <robertmhaas@gmail.com>
Date: 2023-02-21T22:49:37Z
Lists: pgsql-hackers 
On 2/21/23 3:12 PM, Andres Freund wrote:
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>
>
> Hi,
>
> On 2023-02-21 15:00:15 -0600, Jim Nasby wrote:
>> Some food for thought: I think it's also completely fine to extend any
>> relation over a certain size by multiple blocks, regardless of concurrency.
>> E.g. 10 extra blocks on an 80MB relation is 0.1%. I don't have a good feel
>> for what algorithm would make sense here; maybe something along the lines of
>> extend = max(relpages / 2048, 128); if extend < 8 extend = 1; (presumably
>> extending by just a couple extra pages doesn't help much without
>> concurrency).
> I previously implemented just that. It's not easy to get right. You can easily
> end up with several backends each extending the relation by quite a bit, at
> the same time (or you re-introduce contention). Which can end up with a
> relation being larger by a bunch if data loading stops at some point.
>
> We might want that as well at some point, but the approach implemented in the
> patchset is precise and thus always a win, and thus should be the baseline.
Yeah, what I was suggesting would only make sense when there *wasn't* 
contention.

Commits

  1. lwlock: Fix quadratic behavior with very long wait lists

  2. Support RBM_ZERO_AND_CLEANUP_LOCK in ExtendBufferedRelTo(), add tests

  3. Use ExtendBufferedRelTo() in XLogReadBufferExtended()

  4. hio: Use ExtendBufferedRelBy() to extend tables more efficiently

  5. heapam: Pass number of required pages to RelationGetBufferForTuple()

  6. Convert many uses of ReadBuffer[Extended](P_NEW) to ExtendBufferedRel()

  7. Use ExtendBufferedRelTo() in {vm,fsm}_extend()

  8. bufmgr: Introduce infrastructure for faster relation extension

  9. bufmgr: Support multiple in-progress IOs by using resowner

  10. bufmgr: Acquire and clean victim buffer separately

  11. bufmgr: Add Pin/UnpinLocalBuffer()

  12. bufmgr: Add some more error checking [infrastructure] around pinning

  13. Add smgrzeroextend(), FileZero(), FileFallocate()

  14. Don't initialize page in {vm,fsm}_extend(), not needed

  15. bufmgr: Remove buffer-write-dirty tracepoints

  16. hio: Release extension lock before initializing page / pinning VM

  17. bufmgr: Fix undefined behaviour with, unrealistically, large temp_buffers

  18. Fix memory leak and inefficiency in CREATE DATABASE ... STRATEGY WAL_LOG

  19. pgstat: Track more detailed relation IO statistics

  20. Use unnamed POSIX semaphores on Cygwin.

  21. Include RelFileLocator fields individually in BufferTag.