Slony has no mechanisms built in that would artificially limit any bandwidth use. So what you observe must have some other roots.

The slony connections are all regular libpq database connections. So you might test this by using psql or pg_dump running on one of those subscribers, connecting to the appropriate data provider. If that can utilize more bandwidth, then the problem lies within the replica itself and something else must be limiting it from reading from the network faster.


Jan

--
Anyone who trades liberty for security deserves neither liberty nor security. -- Benjamin Franklin 

-----Original Message-----

From:  Stephane LAPIE <stepha at wni.co.jp>
Subj:  [Slony1-general] Slow replication issue
Date:  Fri May 23, 2008 1:37
Size:  1K
To:  slony1-general at lists.slony.info

Hello,

We have been using Slony-I for nearly two years now for our database 
system, with the following cluster :
- 6 Postgres 8.2.4 servers, four in Asia, two in Europe
- Communication occurs over a VPN, and every server can reach the others
- Roundtrip average is 300ms for Europe and Asia servers
- Data providers are in Asia, 3 million row updates / day average 
(mostly split in 4 big updates / day), and at peak time, 100 updates/s

Replication basically occurs fine, to the exception that the European 
servers accumulate lag for around two, three hours (six in worst cases 
observed) when data processing occurs in Asia. We tried raising 
"sync_group_maxsize" in every slon.conf to 24, which diminished the 
number of events replication was lagging behind, but did not diminish 
the lag time (Both are observed through the _SCHEMA.sl_status view, and 
made into a graph through MRTG)

By reducing processed data quantities of 30%, we could reduce the lag 
time by half. We also checked the VPN status, and there is no obvious 
anomaly nor QoS. The only startling point would be that bandwidth usage 
is extremely low, and that reducing processed data quantities did not 
make the bandwidth usage fall any lower.

It looks as though as Slony is actually limiting itself to not over-use 
the network's bandwidth, but actually ends up using nearly nothing. 
Given our current network environment, we could perfectly cope with 
Slony using 10 times more bandwidth with no problem.

Is there a way to force Slony out of it's "don't go too hard on the 
network" mode (such as a setting in slon.conf)?

Thanks in advance,
-- 
Stephane LAPIE
Condapter / WITH EPC / Europe
Weathernews, Inc.
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