checkpoint_segments upgrade recommendation?
The release notes say that checkpoint_segments has been replaced by
max_wal_size and min_wal_size, but there is no indication on how to
convert between the old and new settings. I think a lot of people will
have checkpoint_segments delicately tuned, so we should at least give
them a hint on how to carry that forward in spirit.
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On Fri, Oct 16, 2015 at 2:52 PM, Peter Eisentraut <peter_e@gmx.net> wrote:
The release notes say that checkpoint_segments has been replaced by
max_wal_size and min_wal_size, but there is no indication on how to
convert between the old and new settings. I think a lot of people will
have checkpoint_segments delicately tuned, so we should at least give
them a hint on how to carry that forward in spirit.
Yeah, it would be nice to have some guidance about that. But do we
know what the guidance should be?
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Robert Haas
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On Sat, Oct 17, 2015 at 4:45 AM, Robert Haas <robertmhaas@gmail.com> wrote:
On Fri, Oct 16, 2015 at 2:52 PM, Peter Eisentraut <peter_e@gmx.net> wrote:
The release notes say that checkpoint_segments has been replaced by
max_wal_size and min_wal_size, but there is no indication on how to
convert between the old and new settings. I think a lot of people will
have checkpoint_segments delicately tuned, so we should at least give
them a hint on how to carry that forward in spirit.Yeah, it would be nice to have some guidance about that. But do we
know what the guidance should be?
I think that we should just suggest a reverse formula of the maximum soft
limit of checkpoint_segments for max_wal_size in the release notes of 9.5,
basically:
(3 * your_old_checkpoint_segments + 1) * 16MB = max_wal_size
I am not sure it is worth mentioning that one needs to be be sure to keep
some extra room to handle potential spikes because that's not a hard limit,
but people who have already played with pg_xlog on a different partition
are already aware of that after tuning checkpoint_segments.
min_wal_size is a new parameter though, I don't think it matters much to
hint users for the transfer to the new configuration...
Regards,
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Michael
On 10/17/15 10:25 AM, Michael Paquier wrote:
I think that we should just suggest a reverse formula of the maximum
soft limit of checkpoint_segments for max_wal_size in the release notes
of 9.5, basically:
(3 * your_old_checkpoint_segments + 1) * 16MB = max_wal_size
How about this patch?
(Actually, I'd remove the + 1 to make the numbers come out rounder.)
Attachments:
0001-doc-Add-advice-on-updating-checkpoint_segments-to-ma.patchapplication/x-patch; name=0001-doc-Add-advice-on-updating-checkpoint_segments-to-ma.patchDownload
From ca0ed24ac6a770d637740142a1aed3d76a70a3b3 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter_e@gmx.net>
Date: Tue, 20 Oct 2015 14:09:03 -0400
Subject: [PATCH] doc: Add advice on updating checkpoint_segments to
max_wal_size
---
doc/src/sgml/release-9.5.sgml | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/doc/src/sgml/release-9.5.sgml b/doc/src/sgml/release-9.5.sgml
index d5b68e7..37de29d 100644
--- a/doc/src/sgml/release-9.5.sgml
+++ b/doc/src/sgml/release-9.5.sgml
@@ -153,6 +153,22 @@ <title>Migration to Version 9.5</title>
</listitem>
<listitem>
+ <para>
+ The configuration parameter <varname>checkpoint_segments</varname> has
+ been removed. Its place it taken by the new
+ setting <xref linkend="guc-max-wal-size">. If you had previously
+ tuned <varname>checkpoint_segments</varname>, the following formula will
+ give you an approximately equivalent setting:
+<programlisting>
+max_wal_size = (3 * checkpoint_segments + 1) * 16MB
+</programlisting>
+ Note that the default setting for <varname>max_wal_size</varname> is
+ much higher than the default <varname>checkpoint_segments</varname> used
+ to be, so setting this might no longer be necessary.
+ </para>
+ </listitem>
+
+ <listitem>
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On Wed, Oct 21, 2015 at 3:11 AM, Peter Eisentraut <peter_e@gmx.net> wrote:
On 10/17/15 10:25 AM, Michael Paquier wrote:
I think that we should just suggest a reverse formula of the maximum
soft limit of checkpoint_segments for max_wal_size in the release notes
of 9.5, basically:
(3 * your_old_checkpoint_segments + 1) * 16MB = max_wal_sizeHow about this patch?
(Actually, I'd remove the + 1 to make the numbers come out rounder.)
Removing the + 1 is fine for me.
+ been removed. Its place it taken by the new
"Its place is taken".
Other than those little things this looks fine to me.
Regards,
--
Michael