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) / CheckPointSegments;
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 ?
