Re: Streaming replication

Mike Howland wrote:
> I have two machines where the secondary is configured as a backup of the primary machine.
> I used the instructions here: https://wiki.postgresql.org/wiki/Streaming_Replication
> to establish streaming replication...
> BTW, I'm using the 7.1 path (using backup/rsync/!backup) to prime the files on the secondary machine.
> 
> Most of the time it comes up, connects and is quite happy.
> For my own sanity I have a bit of monitoring code that occasionally injects a change
> on the primary and watches for it to arrive on the secondary to ensure data is flowing.
> I also have some code that checks to see how close things are using pg_current_xlog_location()
> and pg_last_xlog_receive_location().  When things are working, these checks are always fine.
> 
> Once in a while, this nonce value does not seem to be updated on the secondary server
> (although I can see it change on the primary).
> During this period of time, my watcher code also detects that pg_last_xlog_receive_location()
> is ahead of pg_current_xlog_location().  From what I can tell, the secondary has connected to the primary,
> it's just data does not seem to be flowing.  I'll attach a bit of detal below.

The way you initialize the standby looks fine.

One explanation for the delay you observe would be if "max_standby_streaming_delay"
is set greater than zero and there are queries running on the standby that block
application of the changes streamed from the primary.

Yours,
Laurenz Albe