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Re: Idea for nested transactions / savepoints

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Idea for nested transactions / savepoints
Date: 2001-09-06 20:41:33
Message-ID: 200109062041.f86KfY421448@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Added to TODO.detail/transactions as a nested transaction idea.

> > Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)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.
> 
> -- 
>   Bruce Momjian                        |  http://candle.pha.pa.us
>   pgman(at)candle(dot)pha(dot)pa(dot)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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-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman(at)candle(dot)pha(dot)pa(dot)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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