[Bucardo-general] Swap replication latency

Alex Balashov abalashov at evaristesys.com
Sun May 1 10:30:33 UTC 2011


I apologise if this is a poorly researched question;  I looked through 
the list archived extensively and wasn't able to find anything that 
addressed my issue specifically.

I've got a simple swap replication setup between two servers, 
consisting of a single sync of a single herd of a single database 
consisting of about 50 tables and about as many sequences.  Right now, 
it's kind of an active-passive setup, it's just that the slave needs 
to be writable in principle.

Compared to the setups that I'm sure some users of Bucardo are 
running, I wouldn't say it's under a demanding load--maybe 5-6 writes 
transactions/sec at most?  Yet, I am seeing a lag of about 15-20 
minutes until changes on the primary server show up on the secondary.

According to 'bucardo_ctl status <sync name>', I'm getting a "Last 
good" run time between 10 and 12 minutes, and typically involving 
~250/2349/10 Ins/Upd/Del ops.  Ping is on.  Obviously, my logs are 
full of kicks and this message:

   May  1 06:26:59 db Bucardo[28374]: CTL Could not add to q
   Sending manual notification

Is this normal (not the message, the 15-20 minute lag)?  Is there 
anything I can do to speed it up and make the replication process a 
little more timely, if not necessarily real-time?  I have tinkered 
with a few of the options in the config table (i.e. 'bucardo_ctl show 
all'), but without much luck.  They aren't documented anywhere that I 
can find, so I'm reluctant to mess with them too much.

I'm guessing that if there is a solution, it probably involves 
squeezing more out of each sync through increased statement 
length/value tuples, or by somehow further parallelising the sync 
process when it runs.

Any light that can be shed would be deeply appreciated!


-- Alex

Alex Balashov - Principal
Evariste Systems LLC
260 Peachtree Street NW
Suite 2200
Atlanta, GA 30303
Tel: +1-678-954-0670
Fax: +1-404-961-1892
Web: http://www.evaristesys.com/

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