Re: AW: Plans for solving the VACUUM problem

Zeugswetter Andreas SB wrote:

>>> Vadim, can you remind me what UNDO is used for?
>> 
>> 4. Split pg_log into small files with ability to remove old ones (which
>>    do not hold statuses for any running transactions).
> 
> 
> They are already small (16Mb). Or do you mean even smaller ?
> This imposes one huge risk, that is already a pain in other db's. You need
> all logs of one transaction online. For a GigaByte transaction like a bulk
> insert this can be very inconvenient. 
> Imho there should be some limit where you can choose whether you want 
> to continue without the feature (no savepoint) or are automatically aborted.
> 
> In any case, imho some thought should be put into this :-)
> 
> Another case where this is a problem is a client that starts a tx, does one little
> insert or update on his private table, and then sits and waits for a day.
> 
> Both cases currently impose no problem whatsoever.

Correct me if I am wrong, but both cases do present a problem currently 
in 7.1.  The WAL log will not remove any WAL files for transactions that 
are still open (even after a checkpoint occurs).  Thus if you do a bulk 
insert of gigabyte size you will require a gigabyte sized WAL 
directory.  Also if you have a simple OLTP transaction that the user 
started and walked away from for his one week vacation, then no WAL log 
files can be deleted until that user returns from his vacation and ends 
his transaction.

--Barry

> 
> 
> Andreas
> 
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