delta copies

WebTent lists at
Sun Sep 23 22:21:19 GMT 2007

On Sun, 2007-09-23 at 17:46 -0400, Matt McCutchen wrote:
> On 9/23/07, WebTent <lists at> wrote:
> Not necessarily.  Depending on how pg_dump works, it could be that
> small changes to the database are resulting in unnecessarily large
> changes to the dump.  Make sure you are using the uncompressed format
> because most compression algorithms defeat the delta-transfer
> algorithm almost completely.  Then you might take a look at two
> consecutive dumps and check whether records common to both appear in
> the same order in each dump.  (If pg_dump is dumping the records in a
> different order each time, that would also defeat the delta-transfer
> algorithm because no block of several consecutive records could be
> matched.)

Yeah, I understand what you're saying. What blows me away is that I have
cwRsync keeping two MSSQL backups in sync and this works great. Using
Microsoft SQL Server backup makes a binary compressed backup and it
matches data very well and transfers take a fraction of their initial
transfer. But this larger pgsql compressed backup is so different. I
think I've already tried plain text backup, but I will run it tonight
and if it still doesn't match any better, I'll see if I can find out why
on the Postgresql list this week.

Thanks again for the insight!


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