postgrsql 9.5: Old WAL files remain in secondary `pg_xlog`

[Mohan NBSPS <mohan.nbs.ont@xxxxxxxxx>]

Hello Community,

Although the WAL retaining settings are default (max size 1GB),

`wal_keep_segments` is 25, checkpoint target is 2.5 minutes(default).

I noticed a few WAL files in secondary nodes (streaming replication) `pg_xlog`

folder.

What could be the reason why postgresql did not delete these ?

Thank you

Regards

Mohan