On 11/20/2014 11:02 AM, zach cruise wrote:
On 11/20/14, Adrian Klaver <adrian.klaver@xxxxxxxxxxx> wrote:
On 11/20/2014 08:00 AM, zach cruise wrote:
combining replies for the list:
Well it would depend on your setup and the load on the master. Assuming
streaming replication. Simple explanation:
yes streaming replication.
1) If the master is down and slave is up then the slave will stall at
whatever the last WAL was sent. When the master comes back up it will
catch up as new WALs are generated.
2) If the slave is down and the master is up, the master will keep on
creating WALs. The issue is that WALs are recycled over time, so given a
significant load on the master and extended downtime for the slave it is
possible that when the slave comes back up a WAL it needs is no longer
available and it will start throwing errors. One way to tune this is
modify wal_keep_segments (integer):
http://www.postgresql.org/docs/9.3/interactive/runtime-config-replication.html
while the WAL archive directory has to be shared with both master and
slave, should the WAL archive directory be independent of them ie
should it not go down with either of them? if it has to go down with
one, it seems it'd best for the WAL archive directory to go down with
slave?
So I am to understand that you have WAL archiving set up also?
Again a simplified version:
The ideal situation is you have a third machine that has the WAL
archives. The issue is that if the master cannot archive a WAL it will
keep it around until it can. So depending on load and outage you can end
with disk space issues on the master should it not be able clear the WALs.
For more info see:
http://www.postgresql.org/docs/9.3/interactive/continuous-archiving.html
For failover see:
http://www.postgresql.org/docs/9.3/interactive/warm-standby-failover.html
"PostgreSQL does not provide the system software required to identify a
failure on the primary and notify the standby database server. Many such
tools exist and are well integrated with the operating system facilities
required for successful failover, such as IP address migration."
So if you are looking for auto-promote you will need to look at third
party tools or writing your own script.
while i can always use "pg_ctl promote", any recommendations for windows?
Not from me, I do not run Postgres on Windows so I will be of no help there.
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
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