Space Related Errors in Postgres 10.4 Logical Replication

Hi all,

I have configured Postgres Native Logical Replication for 2 servers(a
publisher and subscriber). I have came across a new error in the postgres
log file as shown as below:

*PUBLISHER LOG:*
*2018-08-20 10:34:55.801 IST [24955] user(at)db ERROR: could not create
directory "pg_replslot/mysub_14211111_sync_111111.tmp": No space left on
device *
*2018-08-20 10:34:56.036 IST [34222] user(at)db ERROR: could not create file
"pg_replslot/mysub/state.tmp": No space left on device*
*2018-08-20 10:34:56.053 IST [23444] user(at)db WARNING: could not create
relation-cache initialization file "global/pg_internal.init.11331": No space
left on device*
*2018-08-20 10:34:56.053 IST [23444] user(at)db DETAIL: Continuing anyway, but
there's something wrong.*

My questions are:
1) why has the error occurred?
2) What is the immediate to do task to reduce this error?
3) How to prevent it's forthcoming occurrence (or) How to make changes to
reduce this error?

This is my first Logical Replication setup. Kindly help me with these
issues..

Thanks in Advance.

Regards,
Pavan

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