Re: [HACKERS] [PATCH]make pg_rewind to not copy useless WAL files - Mailing list pgsql-hackers

From Alexander Korotkov
Subject Re: [HACKERS] [PATCH]make pg_rewind to not copy useless WAL files
Date
Msg-id CAPpHfdv_rMGP0M8vo3v2MVq4qeVCMvV10gcMXyHmxkAxK4SR4w@mail.gmail.com
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In response to Re: [HACKERS] [PATCH]make pg_rewind to not copy useless WALfiles  (chenhj <chjischj@163.com>)
Responses Re: [HACKERS] [PATCH]make pg_rewind to not copy useless WALfiles
List pgsql-hackers
On Sat, Sep 30, 2017 at 8:18 PM, chenhj <chjischj@163.com> wrote:
On 2017-09-30 02:17:54,"Alexander Korotkov" <a.korotkov@postgrespro.ruwrote:

Great.  Now code of this patch looks good for me.
However, we forgot about documentation.

  <para>
   The result is equivalent to replacing the target data directory with the
   source one. Only changed blocks from relation files are copied;
   all other files are copied in full, including configuration files. The
   advantage of <application>pg_rewind</> over taking a new base backup, or
   tools like <application>rsync</>, is that <application>pg_rewind</> does
   not require reading through unchanged blocks in the cluster. This makes
   it a lot faster when the database is large and only a small
   fraction of blocks differ between the clusters.
  </para>

At least, this paragraph need to be adjusted, because it states whose files are copied.  And probably latter paragraphs whose state about WAL files.



Your are rigth.
I wrote a draft as following, but i'm afraid whether the english statement is accurate.

I'm not native english speaker too :(

Only the WAL files between the point of divergence and the current WAL insert location of the source server are copied, *for* other WAL files are useless for the target server. 

I'm not sure about this usage of word *for*.  For me, it probably should be just removed.  Rest of changes looks good for me.  Please, integrate them into the patch.

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company 

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