| 50.8. Synchronous Replication Support for Logical Decoding | ||||
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50.8. Synchronous Replication Support for Logical Decoding
50.8.1. Overview
Logical decoding can be used to buildsynchronous replication solutions with the same user interface as synchronous replication forstreaming replication. To do this, the streaming replication interface (seeSection 50.3) must be used to stream out data. Clients have to sendStandby status update (F) (seeSection 54.4) messages, just like streaming replication clients do.
Note
A synchronous replica receiving changes via logical decoding will work in the scope of a single database. Since, in contrast to that,synchronous_standby_names currently is server wide, this means this technique will not work properly if more than one database is actively used.
50.8.2. Caveats
In synchronous replication setup, a deadlock can happen, if the transaction has locked [user] catalog tables exclusively. SeeSection 50.6.2 for information on user catalog tables. This is because logical decoding of transactions can lock catalog tables to access them. To avoid this users must refrain from taking an exclusive lock on [user] catalog tables. This can happen in the following ways:
Issuing an explicit
LOCKonpg_classin a transaction.Perform
CLUSTERonpg_classin a transaction.Executing
TRUNCATEon [user] catalog table in a transaction.
Note that these commands that can cause deadlock apply to not only explicitly indicated system catalog tables above but also to any other [user] catalog table.