Wednesday, September 30, 2020

Fixing language in Pgpool-II 4.2

 The Challenge

 Upcoming Pgpool-II uses more appropriate language for some technical terms. This has been already done in PostgreSQL. Pgpool-II developers think it's a good thing and decided to follow the way. Actual work has been done by Umar Hayat. Challenge is we have to fix not only documentations but configuration parameters and programs. As a result, his patch was quite large: 159 files have been changed, over 2,000 lines were modified.

 Avoiding Some Words

We avoid some words including "master", "slave", "black", "white". We use instead "main", "leader", "primary", "replica" "read", "write" and so on.

Configuration Parameters are Changed

Here is the list of changed configuration parameters.

black_function_list → write_function_list

white_function_list → read_function_list

black_query_pattern → primary_routing_query_pattern

black_memcache_table_list → cache_unsafe_table_list

white_memcache_table_list → cache_safe_table_list


follow_master_command → follow_primary_command

Native replication mode

Pgpool-II has a mode which allows replication by sending identical SQL statement to PostgreSQL servers (thus no streaming replication configuration is neccessary). This mode is called "native replication mode". In this mode "master" (which is the first PostgreSQL node) and "slave" are used to represent the roll of each PostgreSQL server. Pgpool-II 4.2 will use "main" and "replica" instead.


Watchdog is the feature to avoid Pgpool-II's single point of failure. When deploying multiple Pgpool-II servers, they talk each other so that they can elect new leader server when former leader server goes down. We historically called the leader server as "master" and rest of the server as "standby". Now Pgpool-II uses "leader" instead of "master".


The language cleanup may make users migration process from older version of Pgpool-II a little bit harder. But this should have been done someday, and Pgpool-II developers are proud of doing that in this release.

See preview of 4.2 release note for more details (we expect to have Pgpool-II 4.2 release in October 2020).

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