Re: [streaming replication] 9.1.3 streaming replication bug ?

On 4/11/12, 乔志强 <qiaozhiqiang(at)leadcoretech(dot)com> wrote:
>
>> Yes, increase wal_keep_segments. Even if you set wal_keep_segments to 64,
>> the amount of disk space for WAL files is only 1GB, so there is no need to
>> worry so much, I think. No?
>
> But when a transaction larger than 1GB...

Then you may need WAL space larger than 1GB as well. For replication to work,
it seems likely that you may need to have sufficient WAL space to
handle a row, possibly the entire transaction.. But since a single
statement can update thousands or millions of rows, do you always need
enough WAL space to hold the entire transaction?

> So in sync streaming replication, if master delete WAL before sent to the
> only standby, all transaction will fail forever,
> "the master tries to avoid a PANIC error rather than termination of
> replication." but in sync replication, termination of replication is THE
> bigger PANIC error.

That's somewhat debatable. Would I rather have a master that PANICED or
a slave that lost replication? I would choose the latter. A third
option, which
may not even be feasible, would be to have the master fail the
transaction if synchronous replication cannot be achieved, although
that might have negative consequences as well.

> Another question:
> Does master send WAL to standby before the transaction commit ?

That's another question for the core team, I suspect. A related
question is what happens
if there is a rollback?
--
Mike Nolan