Re: [PATCH]make pg_rewind to not copy useless WAL files

From: chenhj <chjischj(at)163(dot)com>
To: "Alexander Korotkov" <a(dot)korotkov(at)postgrespro(dot)ru>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [PATCH]make pg_rewind to not copy useless WAL files
Date: 2017-10-01 17:27:31
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On 2017-10-01 04:09:19,"Alexander Korotkov" <a(dot)korotkov(at)postgrespro(dot)ru> wrote:

On Sat, Sep 30, 2017 at 8:18 PM, chenhj <chjischj(at)163(dot)com> wrote:

On 2017-09-30 02:17:54,"Alexander Korotkov" <a(dot)korotkov(at)postgrespro(dot)ru> wrote:

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

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.

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.

I had removed the *for* , Pleae check the new patch again.

Best Regards,
Chen Huajun

Attachment Content-Type Size
pg_rewind_wal_copy_reduce_v8.patch application/octet-stream 11.6 KB

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