Horton

Re: [HACKERS] WAL logging problem in 9.4.3?

Kyotaro Horiguchi <horikyota.ntt@gmail.com>

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From: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
To: Noah Misch <noah@leadboat.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>, Dmitry Dolgov <9erthalion6@gmail.com>, andrew.dunstan@2ndquadrant.com, hlinnaka@iki.fi, robertmhaas@gmail.com, Michael Paquier <michael@paquier.xyz>
Date: 2019-10-25T13:20:32Z
Lists: pgsql-hackers

Attachments

On Fri, Oct 25, 2019 at 1:13 PM Kyotaro Horiguchi
<horikyota.ntt@gmail.com> wrote:
> Hello. Thanks for the comment.
>
> # Sorry in advance for possilbe breaking the thread.
>
> > MarkBufferDirtyHint() writes WAL even when rd_firstRelfilenodeSubid or
> > rd_createSubid is set; see attached test case.  It needs to skip WAL whenever
> > RelationNeedsWAL() returns false.
>
> Thanks for pointing out that. And the test patch helped me very much.
>
> Most of callers can tell that to the function, but SetHintBits()
> cannot easily. Rather I think we shouldn't even try to do
> that. Instead, In the attached, MarkBufferDirtyHint() asks storage.c
> for sync-pending state of the relfilenode for the buffer. In the
> attached patch (0003) RelFileNodeSkippingWAL loops over pendingSyncs
> but it is called only at the time FPW is added so I believe it doesn't
> affect performance so much. However, we can use hash for pendingSyncs
> instead of liked list. Anyway the change is in its own file
> v21-0003-Fix-MarkBufferDirtyHint.patch, which will be merged into
> 0002.
>
> AFAICS all XLogInsert is guarded by RelationNeedsWAL() or in the
> non-wal_minimal code paths.
>
> > Cylinder and track sizes are obsolete as user-visible concepts.  (They're not
> > onstant for a given drive, and I think modern disks provide no way to read
> > the relevant parameters.)  I like the name "wal_skip_threshold", and my second
>
> I strongly agree. Thanks for the draft. I used it as-is. I don't come
> up with an appropriate second description of the GUC so I just removed
> it.
>
> # it was "For rotating magnetic disks, it is around the size of a
> # track or sylinder."
>
> > the relevant parameters.)  I like the name "wal_skip_threshold", and
> > my second choice would be "wal_skip_min_size".  Possibly documented
> > as follows:
> ..
> > Any other opinions on the GUC name?
>
> I prefer the first candidate. I already used the terminology in
> storage.c and the name fits more to the context.
>
> > * We emit newpage WAL records for smaller size of relations.
> > *
> > * Small WAL records have a chance to be emitted at once along with
> > * other backends' WAL records. We emit WAL records instead of syncing
> > * for files that are smaller than a certain threshold expecting faster
> - * commit. The threshold is defined by the GUC effective_io_block_size.
> + * commit. The threshold is defined by the GUC wal_skip_threshold.

> It's wrong that it also skips changing flags.
> I"ll fix it soon

This is the fixed verison v22.

The attached are:

- v22-0001-TAP-test-for-copy-truncation-optimization.patch
  Same as v20, 21

- v22-0002-Fix-WAL-skipping-feature.patch
  GUC name changed. Same as v21.

- v22-0003-Fix-MarkBufferDirtyHint.patch
  PoC of fixing the function. will be merged into 0002. (New in v21,
fixed in v22)

- v21-0004-Documentation-for-wal_skip_threshold.patch
  GUC name and description changed. (Previous 0003, same as v21)

- v21-0005-Additional-test-for-new-GUC-setting.patch
  including adjusted version of wal-optimize-noah-tests-v3.patch
  Maybe test names need further adjustment. (Previous 0004, same as v21)

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center

Commits

  1. Add perl2host call missing from a new test file.

  2. Skip WAL for new relfilenodes, under wal_level=minimal.

  3. Revert "Skip WAL for new relfilenodes, under wal_level=minimal."

  4. Back-patch log_newpage_range().

  5. During heap rebuild, lock any TOAST index until end of transaction.

  6. In log_newpage_range(), heed forkNum and page_std arguments.

  7. Back-patch src/test/recovery and PostgresNode from 9.6 to 9.5.

  8. Reduce pg_ctl's reaction time when waiting for postmaster start/stop.

  9. Accelerate end-of-transaction dropping of relations

  10. Redesign the planner's handling of index-descent cost estimation.

  11. Make TRUNCATE do truncate-in-place when processing a relation that was created