| From: | Jim Nasby <Jim(dot)Nasby(at)BlueTreble(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Magnus Hagander <magnus(at)hagander(dot)net>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Avoid full page images in streaming replication? |
| Date: | 2015-10-22 22:47:01 |
| Message-ID: | 56296765.2040206@BlueTreble.com |
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| Lists: | pgsql-hackers |
On 10/22/15 5:11 PM, Robert Haas wrote:
> It's true that if the standby didn't have the master's FPIs, it could
> generate its own in some side location that behaves like a separate
> WAL stream or a double-write buffer. But that would be a heck of a
> lot of work to implement for an uncertain benefit.
If the receiver didn't write the WAL before processing it then it can
just stick the page image into the WAL it's writing for itself. Probably
not good for syncrep, but I don't think you'd want this on for syncrep
anyway.
But yes, this is all very hand-wavy without any actual data on what
percentage of the WAL stream is FPIs. Looks like pageinspect doesn't
work for WAL... does anyone have a script/tool that breaks out what
percentage of a WAL file is FPIs?
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com
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