Re: Extending BASE_BACKUP in replication protocol: incremental backup and backup format

<p dir="ltr"><br /> On Jan 14, 2014 2:44 PM, "Andres Freund" <<a
href="mailto:andres@2ndquadrant.com">andres@2ndquadrant.com</a>>wrote:<br /> ><br /> > On 2014-01-14 14:42:36
+0100,Magnus Hagander wrote:<br /> > > On Tue, Jan 14, 2014 at 2:41 PM, Andres Freund <<a
href="mailto:andres@2ndquadrant.com">andres@2ndquadrant.com</a>>wrote:<br/> > ><br /> > > > On
2014-01-1414:40:46 +0100, Magnus Hagander wrote:<br /> > > > > On Tue, Jan 14, 2014 at 2:18 PM, Andres
Freund<<a href="mailto:andres@2ndquadrant.com">andres@2ndquadrant.com</a><br /> > > > >wrote:<br /> >
>> ><br /> > > > > > On 2014-01-14 14:12:46 +0100, Magnus Hagander wrote:<br /> > > >
>> > Either way - if we can do this in a safe way, it sounds like a good<br /> > > > idea.<br /> >
>> > > > It would be sort of like rsync, except relying on the fact that we<br /> > > > can<br
/>> > > > > look<br /> > > > > > > at the LSN and don't have to compare the actual
files,right?<br /> > > > > ><br /> > > > > > Which is an advantage, yes. On the other
hand,it doesn't fix problems<br /> > > > > > with a subtly broken replica, e.g. after a bug in replay,
ordisk<br /> > > > > > corruption.<br /> > > > > ><br /> > > > > ><br />
>> > > Right. But neither does rsync, right?<br /> > > ><br /> > > > Hm? Rsync's really
onlysafe with --checksum and with that it definitely<br /> > > > should fix those?<br /> > > ><br />
>> ><br /> > > I think we're talking about difference scenarios.<br /> ><br /> > Sounds like
it.<br/> ><br /> > > I thought you were talking about a backup taken from a replica, that<br /> > >
alreadyhas corruption. rsync checksums surely aren't going to help with<br /> > > that?<br /> ><br /> > I
wastalking about updating a standby using such an incremental or<br /> > differential backup from the primary (or a
standbyhigher up in the<br /> > cascade). If your standby is corrupted in any way a rsync --checksum<br /> > will
certainlycorrect errors if it syncs from a correct source?<br /><p dir="ltr">Sure, but as I understand it that's not at
allthe scenario that the suggested functionality is for. You can still use rsync for that, I don't think anybody
suggestedremoving that ability. Replicas weren't the target... <p dir="ltr">/Magnus