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Postgres FD Implementation
Commit 1fbb2d9c authored by Bruce Momjian's avatar Bruce Momjian
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Update transactions for nested idea.

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