| From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
|---|---|
| To: | Fujii Masao <masao(dot)fujii(at)gmail(dot)com> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, Hannu Krosing <hannu(at)krosing(dot)net>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Bruce Momjian <bruce(at)momjian(dot)us>, Markus Wanner <markus(at)bluegap(dot)ch>, ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Synchronous Log Shipping Replication |
| Date: | 2008-09-15 14:16:37 |
| Message-ID: | 48CE6E45.1000200@enterprisedb.com |
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| Lists: | pgsql-hackers |
Fujii Masao wrote:
> On Fri, Sep 12, 2008 at 12:17 AM, Heikki Linnakangas
> <heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
>> Hmm. There's more problems than the TLI with that. For the original master
>> to catch up by replaying WAL from the new slave, without restoring from a
>> full backup, the original master must not write to disk *any* WAL that
>> hasn't made it to the slave yet. That is certainly not true for asynchronous
>> replication, but it also throws off the idea of flushing the WAL
>> concurrently to the local disk and to the slave in synchronous mode.
>
> Yes.
>
> If the master fails after writing WAL to disk and before sending it to
> the slave,
> at least latest WAL file would be inconsistent between both servers. So,
> regardless of using a base backup, in a setup procedure, we need to delete
> those inconsistent WAL files or overwrite them.
And if you're unlucky, the changes in the latest WAL file might already
have been flushed to data files as well.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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