Changed default value for `box.cfg.replication_sync_timeout

[TarantoolBot]

Product: Tarantool
Since: 2.11
Root document:

• https://www.tarantool.io/en/doc/latest/reference/configuration/#confval-replication_sync_timeout
• https://www.tarantool.io/en/doc/latest/reference/reference_lua/compat/box_cfg_replication_sync_timeout/

SME: @ sergepetrenko

Details

The default value for replication_sync_timeout configuration option
was changed from 300 seconds to 0.
Requested by @ sergepetrenko in tarantool/tarantool@67cb4e4.

[sergepetrenko]

Please note, the behaviour won't change by default. We decided to add a compat option for it instead: https://www.notion.so/tarantool/d8ef5ccf94614f839f08e3975d28c611?v=5530a11128c54591b8b9a1a7ec5bf2ba&p=2bb3c98ef6b64c88bb1c131dcc16d4fb&pm=c

The compat option (require('tarantool').compat) will be named box_cfg_replication_sync_timeout, and will be "old" (meaning default replication_sync_timeout is 300). The user may also set it to "new", meaning default replication_sync_timeout will be 0.

It's important to set the option before the first box.cfg call in order for it to take effect.

The noticable behaviour change with the new default:
When configuring replication (box.cfg{replication = ...}) box.cfg{} call will return even before the node is synced with other peers listed in box.cfg.replication. This means the node will be in "orphan" state for some period of time after replication is reconfigured. With old behaviour box.cfg{} would return only after the node is synced, meaning it's not "orphan" and is writable.
If one wishes to emulate old behaviour when replication_sync_timeout is 0, he has to issue box.ctl.wait_rw() after box.cfg(). box.ctl.wait_rw() will return only when the reconfigured node becomes writable.