Force WAL cleanup on running instance

Hi,

I am building a docker image with a postgresql 12.2 instance and while
doing so and importing a dump and running some update scripts wal size
is increasing.

When finished I don't need all those wal files anymore and tried to
force the daemon to clean them up and tried this:

select pg_switch_wal();
CHECKPOINT;

and did wait for a minute.

Sometimes it works and wal files are cleaned and moved away so my image
size is way smaller - but it does not happen always in that minute.

So is there a way to tell postgres to force the housekeeping of the wal
stuff via a statement / command line tool?
In a "normal" running instance it just takes care of itself and it will
happen sooner or later and it doesn't really matter when that will
happen - but with my docker image which is automatically build it would
be nice to have a deterministic way of trigger that to reduce the final
size image.

Is there some way to trigger this?

kind regards

Torsten

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