My apologies, I realized I left out the info of my installation. I'm 
running slony 1.2.20, and postgres 8.4.2 on my slave, and 8.4.1 on my 
master.

- Brian

Brian Fehrle wrote:
> Hi all,
>
>     I have a two node slony cluster and I have the slon daemon on the 
> slave node to run with the -a command. I'm attempting to better 
> understand how the logs work for slony log shipping, and have noticed a 
> bit of "odd" behavior (perhaps just odd to me) that perhaps someone can 
> explain to me. It's not just the log shipping that I'd like to better 
> understand, but just how the slony slave and master communicate with 
> eachother and make sure that the slave is in sync with the master, and 
> receiving ALL data that it needs without missing any.
>
> In each of the archive logs created by the slony slave with the -a 
> command, it looks something like this:
>
> ---------------------------------------
>
> ------------------------------------------------------------------
> -- Slony-I log shipping archive
> -- Node 1, Event 555
> ------------------------------------------------------------------
> start transaction;
> select "_slony".archiveTracking_offline('22', '2010-06-01 12:53:11.214886');
> -- end of log archiving header
> ------------------------------------------------------------------
> -- start of Slony-I data
> ------------------------------------------------------------------
> select "_slony".sequenceSetValue_offline(1,'38');
>
>
> ------------------------------------------------------------------
> -- End Of Archive Log
> ------------------------------------------------------------------
> commit;
> vacuum analyze "_slony ".sl_archive_tracking;
>
> ---------------------------------------
>
> Obviously, this log has no actual replication data in it, however there 
> are two main things that I notice in this. First is the Event number, 
> second is the number which is in the select statement for 
> archiveTracking_offline (which is the same number as what is in the name 
> of this particular file, slony1_log_2_00000000000000000022.sql).
>
> For the slony log shipping to work, I understand that each of the log 
> files are required in order, but I've noticed that looking through the 
> actual files, the Events themselves sometimes skip a number, or several. 
> Example,
>
> ---------------------------------------
> # cat /path/to/slon_archive_logs/* | grep Event
> -- Node 1, Event 554
> -- Node 1, Event 555
> -- Node 1, Event 556
> -- Node 1, Event 558
> -- Node 1, Event 559
> ---------------------------------------
>
> Looking at this, event 557 is missing, however the numbering of the 
> archive logs is not broken, each log appears with the expected numbering 
> in the name. This happens often, and I originally thought that this was 
> due to the log that contains the previous event (in this case 556) would 
> contain the data for both events, and 557 would simply not appear. I've 
> looked through every single archive log, and the event does not appear 
> in any of them, nor does it appear later down the road.
>
> I then thought that this event could be an event that isn't a sync, but 
> rather perhaps something else that wouldn't make it into these archive 
> logs (this might still bet he case). However, shortly after seeing that 
> this event is missing, i took a look at the sl_event table and saw that 
> the event is indeed there and is indeed a SYNC:
>
> ---------------------------------------
> postgres=# select ev_seqno, ev_type from _slony.sl_event where ev_origin 
> = '1';
>  ev_seqno | ev_type
> ----------+---------
>   554 | SYNC
>   555 | SYNC
>   556 | SYNC
>   557 | SYNC
>   558 | SYNC
>   559 | SYNC
> ---------------------------------------
>
>
> Basically what I want to do is write up a little script that will alert 
> me via email if something goes wonky with slony replication. I had an 
> event recently where data was missing from the slony slave, and all the 
> searching I could do came up with showed that the data was never 
> replicated, but slony never reported errors (this is in a recent email 
> to this mailing list). It would be easy to raise an alert that says 
> "woah event 557 was not found", however if it is normal behavior for 
> events to be missing like this, then that wouldn't be a good approach to 
> take.
>
> I've seen there are a couple of slony monitoring tools, and I'll be 
> checking them out to see if they offer anything that I could use. But 
> any other suggestions, or even some clarification as to how some of this 
> works would be greatly appreciated. If the situation happens again where 
> my slony slave is missing data, I'd like a bit of logs to review and see 
> when something may have gone wrong, even if i have to generate these 
> logs myself with some sort of monitoring.
>
> Thanks in advance,
>     Brian F
> _______________________________________________
> Slony1-general mailing list
> Slony1-general at lists.slony.info
> http://lists.slony.info/mailman/listinfo/slony1-general
>