multixact's starting offset before the offset has been stored into the
SLRU file. A simple fix would be to hold the MultiXactGenLock until the
offset has been stored, but that looks like a big concurrency hit. Instead
rely on knowledge that unset offsets will be zero, and loop when we see
a zero. This requires a little extra hacking to ensure that zero is never
a valid value for the offset. Problem reported by Matteo Beccati, fix
ideas from Martijn van Oosterhout, Alvaro Herrera, and Tom Lane.
generated from subquery outputs: use the type info stored in the Var
itself. To avoid making ExecEvalVar and slot_getattr more complex
and slower, I split out the whole-row case into a separate ExecEval routine.
type ID information even when it's a record type. This is needed to
handle whole-row Vars referencing subquery outputs. Per example from
Richard Huxton.
This makes the error messages for PREPARE TRANSACTION, COMMIT PREPARED
etc. match the docs, which talk about "transaction identifier" not
"gid" or "global transaction identifier".
Steve Woodcock
the wrong buffer dirty when trying to kill a dead index entry that's on
a page after the one it started on. No risk of data corruption, just
inefficiency, but still a bug.
generated by bitmap index scans. Along the way, simplify and speed up
the code for counting sequential and index scans; it was both confusing
and inefficient to be taking care of that in the per-tuple loops, IMHO.
initdb forced because of internal changes in pg_stat view definitions.
was created on a machine with alignment rules and floating-point format
similar to the current machine. Per recent discussion, this seems like
a good idea with the increasing prevalence of 32/64 bit environments.
on a page, as suggested by ITAGAKI Takahiro. Also, change a few places
that were using some other estimates of max-items-per-page to consistently
use MaxOffsetNumber. This is conservatively large --- we could have used
the new MaxHeapTuplesPerPage macro, or a similar one for index tuples ---
but those places are simply declaring a fixed-size buffer and assuming it
will work, rather than actively testing for overrun. It seems safer to
size these buffers in a way that can't overflow even if the page is
corrupt.
saves nearly 700kB in the default shared memory segment size, which seems
worthwhile, and it is a feature that many users won't use anyway. Per
Heikki's argument, there is no point in a compromise value --- those who
are using 2PC at all will probably want it at least equal to max_connections.
But we can't set it to zero by default without breaking the prepared_xacts
regression test.
after the fact. Fix bug with incorrect test for whether we are at end
of logfile segment. Arrange for writes triggered by XLogInsert's
is-cache-more-than-half-full test to synchronize with the cache boundaries,
so that in long transactions we tend to write alternating halves of the
cache rather than randomly chosen portions of it; this saves one more
write syscall per cache load.
not accepting queries).
errmsg("database is not accepting queries to avoid
wraparound data loss in database \"%s\"",
errhint("Stop the postmaster and use a standalone
backend to VACUUM database \"%s\".",
to 'Size' (that is, size_t), and install overflow detection checks in it.
This allows us to remove the former arbitrary restrictions on NBuffers
etc. It won't make any difference in a 32-bit machine, but in a 64-bit
machine you could theoretically have terabytes of shared buffers.
(How efficiently we could manage 'em remains to be seen.) Similarly,
num_temp_buffers, work_mem, and maintenance_work_mem can be set above
2Gb on a 64-bit machine. Original patch from Koichi Suzuki, additional
work by moi.
insufficient paranoia in code that follows t_ctid links. (We must do both
because even with VACUUM doing it properly, the intermediate state with
a dangling t_ctid link is visible concurrently during lazy VACUUM, and
could be seen afterwards if either type of VACUUM crashes partway through.)
Also try to improve documentation about what's going on. Patch is a bit
bulky because passing the XMAX information around required changing the
APIs of some low-level heapam.c routines, but it's not conceptually very
complicated. Per trouble report from Teodor and subsequent analysis.
This needs to be back-patched, but I'll do that after 8.1 beta is out.
whenever we generate a new OID. This prevents occasional duplicate-OID
errors that can otherwise occur once the OID counter has wrapped around.
Duplicate relfilenode values are also checked for when creating new
physical files. Per my recent proposal.
delay and limit, both as global GUCs and as table-specific entries in
pg_autovacuum. stats_reset_on_server_start is now OFF by default,
but a reset is forced if we did WAL replay. XID-wrap vacuums do not
ANALYZE, but do FREEZE if it's a template database. Alvaro Herrera
ResourceOwner mechanism already released all reference counts for the
cache entries; therefore, we do not need to scan the catcache or relcache
at transaction end, unless we want to do it as a debugging crosscheck.
Do the crosscheck only in Assert mode. This is the same logic we had
previously installed in AtEOXact_Buffers to avoid overhead with large
numbers of shared buffers. I thought it'd be a good idea to do it here
too, in view of Kari Lavikka's recent report showing a real-world case
where AtEOXact_CatCache is taking a significant fraction of runtime.
track shared relations in a separate hashtable, so that operations done
from different databases are counted correctly. Add proper support for
anti-XID-wraparound vacuuming, even in databases that are never connected
to and so have no stats entries. Miscellaneous other bug fixes.
Alvaro Herrera, some additional fixes by Tom Lane.
Also, write multiple WAL buffers out in one write() operation.
ITAGAKI Takahiro
---------------------------------------------------------------------------
> If we disable writeback-cache and use open_sync, the per-page writing
> behavior in WAL module will show up as bad result. O_DIRECT is similar
> to O_DSYNC (at least on linux), so that the benefit of it will disappear
> behind the slow disk revolution.
>
> In the current source, WAL is written as:
> for (i = 0; i < N; i++) { write(&buffers[i], BLCKSZ); }
> Is this intentional? Can we rewrite it as follows?
> write(&buffers[0], N * BLCKSZ);
>
> In order to achieve it, I wrote a 'gather-write' patch (xlog.gw.diff).
> Aside from this, I'll also send the fixed direct io patch (xlog.dio.diff).
> These two patches are independent, so they can be applied either or both.
>
>
> I tested them on my machine and the results as follows. It shows that
> direct-io and gather-write is the best choice when writeback-cache is off.
> Are these two patches worth trying if they are used together?
>
>
> | writeback | fsync= | fdata | open_ | fsync_ | open_
> patch | cache | false | sync | sync | direct | direct
> ------------+-----------+--------+-------+-------+--------+---------
> direct io | off | 124.2 | 105.7 | 48.3 | 48.3 | 48.2
> direct io | on | 129.1 | 112.3 | 114.1 | 142.9 | 144.5
> gather-write| off | 124.3 | 108.7 | 105.4 | (N/A) | (N/A)
> both | off | 131.5 | 115.5 | 114.4 | 145.4 | 145.2
>
> - 20runs * pgbench -s 100 -c 50 -t 200
> - with tuning (wal_buffers=64, commit_delay=500, checkpoint_segments=8)
> - using 2 ATA disks:
> - hda(reiserfs) includes system and wal.
> - hdc(jfs) includes database files. writeback-cache is always on.
>
> ---
> ITAGAKI Takahiro
Tom Lane
Bruce Momjian
Teodor Sigaev
Neil Conway
Tatsuo Ishii