From: | "Tsunakawa, Takayuki" <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com> |
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To: | 'Narayanan V' <vnarayanan(dot)email(at)gmail(dot)com>, "adelino(dot)j(dot)silva(at)googlemail(dot)com" <adelino(dot)j(dot)silva(at)googlemail(dot)com> |
Cc: | "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | RE: WAL archive (archive_mode = always) ? |
Date: | 2018-10-23 05:33:29 |
Message-ID: | 0A3221C70F24FB45833433255569204D1FAE5C91@G01JPEXMBYT05 |
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Lists: | pgsql-hackers |
From: Narayanan V [mailto:vnarayanan(dot)email(at)gmail(dot)com]
> I think what Takayuki is trying to say is that streaming replication works
> by sending the contents of the WAL archives to the standbys. If archive_mode
> was NOT set to always, and if you wanted to archive WAL logs in the standby
> you would need to rely on the process_command and make it ship the WAL logs
> (to the standby). This causes the same WAL log information to be shipped
> in two places,
>
> 1. Through Streaming Replication
> 2. By the process_command
>
> This redundant shipping of the same information is expensive and consumes
> network bandwidth. This can be avoided with the use of archive_mode=always.
>
> archive_mode=always makes the standby archive the WAL logs it receives,
> thus avoiding the requirement of having to ship it separately.
Exactly. (archive_command, not process_command)
Thanks, Narayanan.
Regards
Takayuki Tsunakawa
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