Hot standby and xlog on a ramdisk

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On 02/04/2016 09:15 AM, Tore Halvorsen wrote:

Hi,

Can a hot standby run correctly with the xlog-files on a ramdisk?

Yes, but, if you lose any, you'll need to rebuild the standby.

-- Eld på åren og sol på eng gjer mannen fegen og fjåg. [Jøtul]
<demo> Tore Halvorsen || +052 0553034554

- --
Scott Mead
OpenSCG <http://www.openscg.com&gt;
http://www.openscg.com
PostgreSQL, Java & Linux Experts
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On 02/04/2016 09:15 AM, Tore Halvorsen wrote:

Can a hot standby run correctly with the xlog-files on a ramdisk?

Yes, but, if you lose any, you'll need to rebuild the standby.

Even if the master and archive contain all the wal files?

--
Eld på åren og sol på eng gjer mannen fegen og fjåg. [Jøtul]
<demo> Tore Halvorsen || +052 0553034554

On 02/04/2016 09:25 AM, Tore Halvorsen wrote:

On 02/04/2016 09:15 AM, Tore Halvorsen wrote:

Can a hot standby run correctly with the xlog-files on a ramdisk?

Yes, but, if you lose any, you'll need to rebuild the standby.

Even if the master and archive contain all the wal files?

If you have the file somewhere, you're okay, whether it's on the master,
standby or an archive host. If you're using log-shipping, you'll need
all the WALs.

--
Eld på åren og sol på eng gjer mannen fegen og fjåg. [Jøtul]
<demo> Tore Halvorsen || +052 0553034554

--
Scott Mead
OpenSCG <http://www.openscg.com&gt;
http://www.openscg.com
PostgreSQL, Java & Linux Experts

On Thu, Feb 4, 2016 at 3:30 PM, Scott R Mead <scottm@openscg.com> wrote:

Can a hot standby run correctly with the xlog-files on a ramdisk?

Yes, but, if you lose any, you'll need to rebuild the standby.

Even if the master and archive contain all the wal files?

If you have the file somewhere, you're okay, whether it's on the master,
standby or an archive host. If you're using log-shipping, you'll need all
the WALs.

So, just to verify my understanding. Using a ramdisk for pg_xlog on a hot
standby slave should be ok in all cases as long as the archive and master
retains all wal files that are not applied?

I maintain a fairly active database (>100GB of wal files every day) and
putting the wal files on a ramdisk (only for the slaves of course) helped
quite a lot.

--
Eld på åren og sol på eng gjer mannen fegen og fjåg. [Jøtul]
<demo> Tore Halvorsen || +052 0553034554

On 2/4/16 9:46 AM, Tore Halvorsen wrote:

On Thu, Feb 4, 2016 at 3:30 PM, Scott R Mead <scottm@openscg.com
<mailto:scottm@openscg.com>> wrote:

Can a hot standby run correctly with the xlog-files on a

ramdisk?

Yes, but, if you lose any, you'll need to rebuild the standby.

Even if the master and archive contain all the wal files?

If you have the file somewhere, you're okay, whether it's on the
master, standby or an archive host. If you're using log-shipping,
you'll need all the WALs.

So, just to verify my understanding. Using a ramdisk for pg_xlog on a
hot standby slave should be ok in all cases as long as the archive and
master retains all wal files that are not applied?

Yes. If the pg_xlog ramdisk is lost on the standby then Postgres will
start throwing errors but there will be no corruption of the heap. It's
possible that Postgres will terminate at this point, but after
remounting the ramdisk you can restart Postgres on the standby and
everything will be fine.

If something goes really horribly wrong you can always rebuild the standby.

--
-David
david@pgmasters.net