I am using a hot_standby setup on PostgreSQL 9.1
While I was testing, I found out that only checkpoint_timeout (+ a
checkpoint since the last restart point) could trigger a restart point.

The code (bgwriter.c) seems to confirm this:

    * Check progress against WAL segments written and checkpoint_segments.
    * We compare the current WAL insert location against the location
    * computed before calling CreateCheckPoint. The code in XLogInsert that
    * actually triggers a checkpoint when checkpoint_segments is exceeded
    * compares against RedoRecptr, so this is not completely accurate.
    * However, it's good enough for our purposes, we're only calculating an
    * estimate anyway.
    if (!RecoveryInProgress())  ===> Only in case of primary
                   recptr = GetInsertRecPtr();
                   elapsed_xlogs =
                                   (((double) (int32) (recptr.xlogid -
ckpt_start_recptr.xlogid)) * XLogSegsPerFile +
                                   ((double) recptr.xrecoff - (double)
ckpt_start_recptr.xrecoff) / XLogSegSize) /

                   if (progress < elapsed_xlogs)  ===> progress in volume
                                   ckpt_cached_elapsed = elapsed_xlogs;
                                   return false;

    * Check progress against time elapsed and checkpoint_timeout.
    gettimeofday(&now, NULL);
    elapsed_time = ((double) ((pg_time_t) now.tv_sec - ckpt_start_time) +

now.tv_usec / 1000000.0) / CheckPointTimeout;

    if (progress < elapsed_time)  ===> progress in time
                   ckpt_cached_elapsed = elapsed_time;
                   return false;

    /* It looks like we're on schedule. */
    return true;

I also found a post from Simon Riggs [1]: "checkpoint_segments is ignored
on standby."

The documentation is stating the opposite [2]: "In standby mode, a
restartpoint is also triggered if checkpoint_segments log segments have
been replayed since last restartpoint and at least one checkpoint record
has been replayed."

Since I am not a native english speaker, maybe I misunderstood the
documentation. But to me, it looks wrong.
If it's indeed wrong. Could you explain why checkpoint_segments doesn't
trigger a restart_point in standby mode ?

Thank you

[2] http://www.postgresql.org/docs/9.1/static/wal-configuration.html

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