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Streaming Replication delay getting bigger - Mailing list pgsql-general

From Patrick B
Subject Streaming Replication delay getting bigger
Date
Msg-id CAJNY3isU461ZYn+zitSZTroTOj9AeM=CmSet0_UCn+k0Gm1jrw@mail.gmail.com
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Responses Re: Streaming Replication delay getting bigger
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Hi guys,

I've got some database servers in USA (own data center) and also @ AWS Japan.

USA:
master01
slave01 (Streaming Replication from master01 + wal_files)
slave02 (Streaming Replication from master01 + wal_files)

Japan: (Cascading replication)
slave03 (Streaming Replication from slave02 + wal_files)
slave04 (Streaming Replication from slave02)

Running this query on slave02:

select now() - pg_last_xact_replay_timestamp() AS replication_delay;
 replication_delay
-------------------
 00:00:00.802012
(1 row)

Same query on slave03 and slave04:

select now() - pg_last_xact_replay_timestamp() AS replication_delay;
 replication_delay
-------------------
 00:56:53.639516
(1 row)

slave02:
SELECT client_hostname    , client_addr    , pg_xlog_location_diff(pg_stat_replication.sent_location, pg_stat_replication.replay_location) AS byte_lag FROM pg_stat_replication;
 client_hostname |  client_addr  | byte_lag
-----------------+---------------+----------
                 | slave03  |  2097400
                 | slave04 |  3803888
(2 rows)


Why is that delay that big? Is it because networking issue? I tried to find out what the cause is, but couldn't find anything.

SCP and FTP (big files) between those servers are really fast, +1.0MB/s.
I'm using PostgreSQL 9.2.14

Thanks!
Patrick.

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