Re: Idea for nested transactions / savepoints

> 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.

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
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