PostgreSQL 9.3 has two key software updates making switchover/switchback easier in High Availability configurations.
First, let’s address the software patches and their descriptions:
1. First patch was committed by Fujii Masao.
Patch commit# 985bd7d49726c9f178558491d31a570d47340459
With this patch, the walsender process tries to send all outstanding WAL records to the standby in replication when the user shuts down the master.
a. All WAL records are synced between two servers after the clean shutdown of the master
b. After promoting the standby to new master, the user can restart the stopped master as new standby without a fresh backup from new master.
2. Second patch was committed by Heikki Linnakangas in PostgreSQL 9.3.
Patch commit# abfd192b1b5ba5216ac4b1f31dcd553106304b19
Before PostgreSQL version 9.3, streaming replication used to stop replicating if the timeline on the primary didn’t match the standby. This generally happens when the user promotes one of the standbys to become the new master. Promoting a standby always results in an increment of timeline ID and after that increment, other standbys will refuse to continue replicating.
With this patch in PostgreSQL 9.3, the standby asks the primary for any timeline history files that are missing from the standby when it connects – if the standby recovery.conf file has the following setting:
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