box.ctl submodule contains two functions:
(wait until read-only)
wait_rw (wait until read-write).
The functions are useful during initialization of a server.
A particular use is for box.once().
For example, when a replica is initializing, it may call
box.once() function while the server is still in
read-only mode, and fail to make changes that are necessary
only once before the replica is fully initialized.
This could cause conflicts between a master and a replica
if the master is in read-write mode and the replica is in
Waiting until “read only mode = false” solves this problem.
To see whether a function is already in read-only or read-write mode, check box.info.ro.
Below is a list of all
|box.ctl.on_schema_init()||Create a “schema_init trigger”|
|box.ctl.on_shutdown()||Create a “shutdown trigger”|