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Update transactions for nested idea.
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Bruce Momjian
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@ -1053,3 +1053,190 @@ ncm@zembu.com
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>
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> regards, tom lane
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From pgsql-hackers-owner+M11649@postgresql.org Wed Aug 1 15:22:46 2001
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From: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
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To: "'pgsql-hackers@postgresql.org'" <pgsql-hackers@postgresql.org>
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Subject: [HACKERS] Using POSIX mutex-es
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Date: Wed, 1 Aug 2001 12:04:24 -0700
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Status: OR
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1. Just changed
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TAS(lock) to pthread_mutex_trylock(lock)
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S_LOCK(lock) to pthread_mutex_lock(lock)
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S_UNLOCK(lock) to pthread_mutex_unlock(lock)
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(and S_INIT_LOCK to share mutex-es between processes).
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2. pgbench was initialized with scale 10.
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SUN WS 10 (512Mb), Solaris 2.6 (I'm unable to test on E4500 -:()
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-B 16384, wal_files 8, wal_buffers 256,
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checkpoint_segments 64, checkpoint_timeout 3600
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50 clients x 100 transactions
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(after initialization DB dir was saved and before each test
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copyed back and vacuum-ed).
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3. No difference.
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Mutex version maybe 0.5-1 % faster (eg: 37.264238 tps vs 37.083339 tps).
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So - no gain, but no performance loss "from using pthread library"
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(I've also run tests with 1 client), at least on Solaris.
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And so - looks like we can use POSIX mutex-es and conditional variables
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(not semaphores; man pthread_cond_wait) and should implement light lmgr,
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probably with priority locking.
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Vadim
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From pgsql-hackers-owner+M11790@postgresql.org Sun Aug 5 14:41:34 2001
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Sun, 5 Aug 2001 14:30:43 -0400 (EDT)
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From: Bruce Momjian <pgman@candle.pha.pa.us>
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Message-ID: <200108051830.f75IUhM25071@candle.pha.pa.us>
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Subject: Re: [HACKERS] Idea for nested transactions / savepoints
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In-Reply-To: <8173.997022088@sss.pgh.pa.us> "from Tom Lane at Aug 5, 2001 10:34:48
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am"
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To: Tom Lane <tgl@sss.pgh.pa.us>
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Date: Sun, 5 Aug 2001 14:30:43 -0400 (EDT)
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cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
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Status: OR
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> Bruce Momjian <pgman@candle.pha.pa.us> writes:
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> > My idea is that we not put UNDO information into WAL but keep a List of
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> > rel ids / tuple ids in the memory of each backend and do the undo inside
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> > the backend.
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>
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> The complaints about WAL size amount to "we don't have the disk space
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> to keep track of this, for long-running transactions". If it doesn't
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> fit on disk, how likely is it that it will fit in memory?
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Sure, we can put on the disk if that is better. I thought the problem
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with WAL undo is that you have to keep UNDO info around for all
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transactions that are older than the earliest transaction. So, if I
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start a nested transaction, and then sit at a prompt for 8 hours, all
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WAL logs are kept for 8 hours.
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We can create a WAL file for every backend, and record just the nested
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transaction information. In fact, once a nested transaction finishes,
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we don't need the info anymore. Certainly we don't need to flush these
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to disk.
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--
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Bruce Momjian | http://candle.pha.pa.us
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pgman@candle.pha.pa.us | (610) 853-3000
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+ If your life is a hard drive, | 830 Blythe Avenue
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+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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From pgman Sun Aug 5 21:16:32 2001
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Sun, 5 Aug 2001 21:16:32 -0400 (EDT)
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From: Bruce Momjian <pgman>
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Message-ID: <200108060116.f761GWH11356@candle.pha.pa.us>
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Subject: Re: [HACKERS] Idea for nested transactions / savepoints
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In-Reply-To: <200108051938.f75Jchi27522@candle.pha.pa.us> "from Bruce Momjian
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at Aug 5, 2001 03:38:43 pm"
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To: Bruce Momjian <pgman@candle.pha.pa.us>
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Date: Sun, 5 Aug 2001 21:16:32 -0400 (EDT)
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cc: Tom Lane <tgl@sss.pgh.pa.us>,
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PostgreSQL-development <pgsql-hackers@postgresql.org>
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Status: OR
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> > Bruce Momjian <pgman@candle.pha.pa.us> writes:
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> > >> The complaints about WAL size amount to "we don't have the disk space
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> > >> to keep track of this, for long-running transactions". If it doesn't
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> > >> fit on disk, how likely is it that it will fit in memory?
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> >
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> > > Sure, we can put on the disk if that is better.
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> >
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> > I think you missed my point. Unless something can be done to make the
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> > log info a lot smaller than it is now, keeping it all around until
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> > transaction end is just not pleasant. Waving your hands and saying
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> > that we'll keep it in a different place doesn't affect the fundamental
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> > problem: if the transaction runs a long time, the log is too darn big.
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>
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> When you said long running, I thought you were concerned about long
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> running in duration, not large transaction. Long duration in one-WAL
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> setup would cause all transaction logs to be kept. Large transactions
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> are another issue.
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>
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> One solution may be to store just the relid if many tuples are modified
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> in the same table. If you stored the command counter for start/end of
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> the nested transaction, it would be possible to sequential scan the
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> table and undo all the affected tuples. Does that help? Again, I am
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> just throwing out ideas here, hoping something will catch.
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Actually, we need to keep around nested transaction UNDO information
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only until the nested transaction exits to the main transaction:
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BEGIN WORK;
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BEGIN WORK;
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COMMIT;
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-- we can throw away the UNDO here
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BEGIN WORK;
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BEGIN WORK;
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...
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COMMIT
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COMMIT;
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-- we can throw away the UNDO here
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COMMIT;
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We are using the outside transaction for our ACID capabilities, and just
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using UNDO for nested transaction capability.
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--
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Bruce Momjian | http://candle.pha.pa.us
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pgman@candle.pha.pa.us | (610) 853-3000
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+ If your life is a hard drive, | 830 Blythe Avenue
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+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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