On 21/10/2019 12:10, Avinash Kumar wrote:
On Mon, Oct 21, 2019 at 4:19 PM Fabio Ugo Venchiarutti
<f.venchiarutti@xxxxxxxxx <mailto:f.venchiarutti@xxxxxxxxx>> wrote:
On 21/10/2019 09:52, Luca Ferrari wrote:
> On Sat, Oct 19, 2019 at 7:46 PM Daulat Ram
<Daulat.Ram@xxxxxxxxxxxxxxx <mailto:Daulat.Ram@xxxxxxxxxxxxxxx>> wrote:
>> One more questions is, how backups are useful if we have
streaming replication . As I know, we can promote the standby as
primary in case of disaster at primary side. Do we need to schedule
backups if we have streaming replication?
>
> Let's speculate a little on that: do you need backups if you have a
> RAID-1 configuration?
> Replication helps you reduce almost to zero the time to handle a
> disaster, backups allow you to recover in a more large time window.
>
> Luca
>
>
TBH I hear this argument more often than I wish.
Offline backups and data replication are nearly entirely orthogonal.
Any form of instantaneous redundancy (RAID, instantaneous replication
and so on) primary is a mitigation measure to protect data &
availability against loss of infrastructure.
Backups (preferably with PITR) also do that, but that's not their
primary purpose unless you can't afford live redundancy on top of them.
Offline backups address many failure scenarios that any form of live
replication is defenseless against (eg: logical damage to the data as a
result of human errors/bugs/vandalism would hit all your replicas, but
you always can perform DR from a backup).
I think we are way ahead of the days where we need to live on Offline
backups involving downtimes.
Today, we have several Online Consistent Backup solutions such as
pg_basebackup (built-in with PG), pgBackRest, BARMAN, WAL-G etc ....
Online Consistent Backups + Archiving of WALs are perfectly reliable.
We need to ensure that we have safe backup locations, for example, push
them to AWS S3 and forget about redundancy.
Why do you think only Offline Backups are reliable today ?
Delayed replicas, or any online rollback capability (such as pg_rewind
off the server's own pg_wal or Oracle's flashback), somewhat live in a
grey area in between, and their effectiveness varies depending on which
level was compromised.
What if you delay your replica by a day, before you making a change
tomorrow (that may need a rollback). Delayed Replica is for emergencies
IMO and of course does not satisfy every possible scenario.
Trade-offs come down to individual implementers, so fair enough.
Our biases must come from different use cases/experience: a good
fraction of recovery/sanitisation operations I had to carry out were
very selective/application specific and involved buildup of anomalies
over time, sometimes months.
Wouldn't have been possible without an old frozen reference for users to
compare with, and that hat to come from very cold storage.
--
Regards
Fabio Ugo Venchiarutti
OSPCFC Network Engineering Dpt.
Ocado Technology
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