On 1/18/17 3:12 PM, Stephen Frost wrote:
> I don't understand what I'm missing when it comes to checkpoint_timeout
> and the time required to recover from a crash.  You aren't the first
> person to question that association, but it seems pretty clear to me.
> When doing recovery, we have to replay everything since the last
> checkpoint.  If we are checkpointing at least every 5 minutes then we
> can't have any more than 5 minutes worth of WAL to replay, right?

But writing WAL and replaying WAL are two entirely different operations.
 Writing a WAL record involves writing a few bytes sequentially.
Replaying a WAL record might involve hopping all over the system and
applying the changes that the WAL record describes.

Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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