pgsql: Skip WAL for new relfilenodes, under wal_level=minimal.

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pgsql: Skip WAL for new relfilenodes, under wal_level=minimal.

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

Until now, only selected bulk operations (e.g. COPY) did this.  If a
given relfilenode received both a WAL-skipping COPY and a WAL-logged
operation (e.g. INSERT), recovery could lose tuples from the COPY.  See
src/backend/access/transam/README section "Skipping WAL for New
RelFileNode" for the new coding rules.  Maintainers of table access
methods should examine that section.

To maintain data durability, just before commit, we choose between an
fsync of the relfilenode and copying its contents to WAL.  A new GUC,
wal_skip_threshold, guides that choice.  If this change slows a workload
that creates small, permanent relfilenodes under wal_level=minimal, try
adjusting wal_skip_threshold.  Users setting a timeout on COMMIT may
need to adjust that timeout, and log_min_duration_statement analysis
will reflect time consumption moving to COMMIT from commands like COPY.

Internally, this requires a reliable determination of whether
RollbackAndReleaseCurrentSubTransaction() would unlink a relation's
current relfilenode.  Introduce rd_firstRelfilenodeSubid.  Amend the
specification of rd_createSubid such that the field is zero when a new
rel has an old rd_node.  Make relcache.c retain entries for certain
dropped relations until end of transaction.

Back-patch to 9.5 (all supported versions).  This introduces a new WAL
record type, XLOG_GIST_ASSIGN_LSN, without bumping XLOG_PAGE_MAGIC.  As
always, update standby systems before master systems.  This changes
sizeof(RelationData) and sizeof(IndexStmt), breaking binary
compatibility for affected extensions.  (The most recent commit to
affect the same class of extensions was
089e4d405d0f3b94c74a2c6a54357a84a681754b.)

Kyotaro Horiguchi, reviewed (in earlier, similar versions) by Robert
Haas.  Heikki Linnakangas and Michael Paquier implemented earlier
designs that materially clarified the problem.  Reviewed, in earlier
designs, by Andrew Dunstan, Andres Freund, Alvaro Herrera, Tom Lane,
Fujii Masao, and Simon Riggs.  Reported by Martijn van Oosterhout.

Discussion: https://postgr.es/m/20150702220524.GA9392@...

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/cb2fd7eac285b1b0a24eeb2b8ed4456b66c5a09f

Modified Files
--------------
contrib/pg_visibility/expected/pg_visibility.out |  35 +++
contrib/pg_visibility/sql/pg_visibility.sql      |  19 ++
doc/src/sgml/config.sgml                         |  39 ++-
doc/src/sgml/perform.sgml                        |  47 +--
src/backend/access/gist/gistutil.c               |  31 +-
src/backend/access/gist/gistxlog.c               |  21 ++
src/backend/access/heap/heapam.c                 |  45 +--
src/backend/access/heap/heapam_handler.c         |  22 +-
src/backend/access/heap/rewriteheap.c            |  21 +-
src/backend/access/nbtree/nbtsort.c              |  41 +--
src/backend/access/rmgrdesc/gistdesc.c           |   6 +
src/backend/access/transam/README                |  45 ++-
src/backend/access/transam/xact.c                |  15 +
src/backend/access/transam/xlogutils.c           |  18 +-
src/backend/bootstrap/bootparse.y                |   4 +
src/backend/catalog/storage.c                    | 246 ++++++++++++++-
src/backend/commands/cluster.c                   |  19 ++
src/backend/commands/copy.c                      |  58 +---
src/backend/commands/createas.c                  |  11 +-
src/backend/commands/indexcmds.c                 |   2 +
src/backend/commands/matview.c                   |  12 +-
src/backend/commands/tablecmds.c                 |  26 +-
src/backend/nodes/copyfuncs.c                    |   2 +
src/backend/nodes/equalfuncs.c                   |   2 +
src/backend/nodes/outfuncs.c                     |   2 +
src/backend/parser/gram.y                        |   4 +
src/backend/parser/parse_utilcmd.c               |   4 +
src/backend/storage/buffer/bufmgr.c              | 125 +++++++-
src/backend/storage/lmgr/lock.c                  |  12 +
src/backend/storage/smgr/md.c                    |  36 ++-
src/backend/storage/smgr/smgr.c                  |  35 +++
src/backend/utils/cache/relcache.c               | 268 ++++++++++++----
src/backend/utils/misc/guc.c                     |  12 +
src/backend/utils/misc/postgresql.conf.sample    |   1 +
src/include/access/gist_private.h                |   2 +
src/include/access/gistxlog.h                    |   1 +
src/include/access/heapam.h                      |   3 -
src/include/access/rewriteheap.h                 |   2 +-
src/include/access/tableam.h                     |  15 +-
src/include/catalog/storage.h                    |   6 +
src/include/nodes/parsenodes.h                   |   3 +
src/include/storage/bufmgr.h                     |   4 +
src/include/storage/lock.h                       |   3 +
src/include/storage/smgr.h                       |   1 +
src/include/utils/rel.h                          |  55 +++-
src/include/utils/relcache.h                     |   8 +-
src/test/recovery/t/018_wal_optimize.pl          | 372 +++++++++++++++++++++++
src/test/regress/expected/alter_table.out        |   6 +
src/test/regress/expected/create_table.out       |  13 +
src/test/regress/sql/alter_table.sql             |   7 +
src/test/regress/sql/create_table.sql            |  15 +
51 files changed, 1439 insertions(+), 363 deletions(-)

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Re: pgsql: Skip WAL for new relfilenodes, under wal_level=minimal.

Tom Lane-2
Noah Misch <[hidden email]> writes:
> Skip WAL for new relfilenodes, under wal_level=minimal.

Various buildfarm members seem not happy with this,
though it's not universal.

Also, given the invasiveness of the patch, I'm quite astonished
that you chose to back-patch it.  Is this really worth ABI
breakage risks in the back branches?

                        regards, tom lane


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Re: pgsql: Skip WAL for new relfilenodes, under wal_level=minimal.

Noah Misch-2
On Sat, Mar 21, 2020 at 03:04:51PM -0400, Tom Lane wrote:
> Noah Misch <[hidden email]> writes:
> > Skip WAL for new relfilenodes, under wal_level=minimal.
>
> Various buildfarm members seem not happy with this,
> though it's not universal.

Yeah, see the main thread:
https://postgr.es/m/20200321190127.GA1763544%40rfd.leadboat.com

> Also, given the invasiveness of the patch, I'm quite astonished
> that you chose to back-patch it.  Is this really worth ABI
> breakage risks in the back branches?

A month ago (https://postgr.es/m/20200219074452.GA4006615@...), I
invited folks to talk me out of back-patching it.  Nobody commented either
way, so I back-patched.  Please reply to that message if you see a reason to
revert the back-patches.  I found only one pgxn extension ("citus") that I
expect to notice the ABI break (change in structure size), and
089e4d405d0f3b94c74a2c6a54357a84a681754b changed the size of the same
structure.  Hence, I'm not worrying about the ABI aspect.  I'm more worried
that some defect that evades testing will corrupt more data than the original
bug.  I don't have any specific kind of defect in mind, though.