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

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От Alexander Korotkov
Тема Re: [HACKERS] [PATCH]make pg_rewind to not copy useless WAL files
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Msg-id CAPpHfdsmBjtQDbAUzTQJZ9Jnpj7aT8n=oPHtiKB=bJ0yedTwGQ@mail.gmail.com
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Ответ на Re: [HACKERS] [PATCH]make pg_rewind to not copy useless WALfiles  (chenhj <chjischj@163.com>)
Ответы Re: [HACKERS] [PATCH]make pg_rewind to not copy useless WALfiles  (chenhj <chjischj@163.com>)
Список pgsql-hackers
On Thu, Sep 28, 2017 at 10:52 PM, chenhj <chjischj@163.com> wrote:
On 2017-09-29 00:43:18,"Alexander Korotkov" <a.korotkov@postgrespro.ru> wrote:
On Thu, Sep 28, 2017 at 6:44 PM, chenhj <chjischj@163.com> wrote:
On 2017-09-28 01:29:29,"Alexander Korotkov" <a.korotkov@postgrespro.ru> wrote:
It appears that your patch conflicts with fc49e24f.  Please, rebase it.

Yes, i had rebased it, Please check the new patch. 

Good, now it applies cleanly.

else if (strncmp(path, XLOGDIR"/", strlen(XLOGDIR"/")) == 0 &&
 IsXLogFileName(path + strlen(XLOGDIR"/")) &&
 (strcmp(path + strlen(XLOGDIR"/") + 8, divergence_wal_filename + 8) < 0 ||
  strcmp(path + strlen(XLOGDIR"/") + 8, last_source_wal_filename + 8) > 0))

According to our conding style, you should leave a space betwen XLOGDIF and "/".
Also, you do a trick by comparison xlog segment numbers using strcmp().  It's nice, but I would prefer seeing XLogFromFileName() here.  It would improve code readability and be less error prone during further modifications.

Thanks for advice!
I had modified it.

OK. Patch becomes better.
I also have more general question.  Why do we need upper bound for segment number (last_source_segno)?  I understand the purpose of lower bound (divergence_segno) which save us from copying extra WAL files, but what is upper bound for?  As I understood, we anyway need to replay most recent WAL records to reach consistent state after pg_rewind.  I propose to remove last_source_segno unless I'm missing something.


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

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