replication recovery/startup question

Hi,

I started replicating my Postgres9.1.3 server on Friday, and it seems to be working well.
The master server database is quite large (somewhere in the order of 85GB) so the rsync to copy the base_backup took a while to complete.

However, looking at the log files and 'ps' I'm wondering if the replication has caught up or is still catching up.

Master :
postgres 3964 3926 0 Jun21 ? 00:00:32 postgres: archiver process last was 000000010000003D00000055
postgres 15080 3926 0 Jun22 ? 00:02:39 postgres: wal sender process dbrepl xxx.xxx.xxx.xxx(46496) streaming 3D/560752D0

Slave :
postgres 5048 5040 0 Jun22 ? 00:11:37 postgres: startup process recovering 000000010000003D00000056
postgres 6714 5040 0 Jun22 ? 00:06:24 postgres: wal receiver process streaming 3D/560752D0

The log files in ~data/pg_xlog show :

ls -lart
<list truncated>
-rw------- 1 postgres postgres 16777216 Jun 25 13:36 000000010000003F0000004C
-rw------- 1 postgres postgres 16777216 Jun 25 13:36 000000010000003F0000004D
-rw------- 1 postgres postgres 16777216 Jun 25 13:37 000000010000003F00000050
-rw------- 1 postgres postgres 16777216 Jun 25 13:46 000000010000003F00000052
-rw------- 1 postgres postgres 16777216 Jun 25 14:24 000000010000003F00000053
-rw------- 1 postgres postgres 16777216 Jun 25 14:50 000000010000003F00000054
-rw------- 1 postgres postgres 16777216 Jun 25 14:59 000000010000003F00000055
-rw------- 1 postgres postgres 16777216 Jun 25 15:03 000000010000003F00000056
-rw------- 1 postgres postgres 16777216 Jun 25 15:06 000000010000003F00000057
-rw------- 1 postgres postgres 16777216 Jun 25 15:10 000000010000003F00000058
drwx------ 4 postgres postgres 69632 Jun 25 15:24 .
-rw------- 1 postgres postgres 16777216 Jun 25 15:29 000000010000003D00000055
-rw------- 1 postgres postgres 16777216 Jun 25 15:30 000000010000003D00000056

Why would the output from 'ls' show older filenames (0....1....3D...xx) as newer in date than the "0....1....3F...xx" filenames?
Does Postgres re-cycle old log filenames ?

Does the output from 'ps' mean the master/slave are in sync, or is the slave really still playing catchup (based on the names of the logfiles in pg_xlog) ?

Cheers,
Rob.