when does druid delete file from basePersist,I have so many file in realtime basePersist dir

[492066199]

I set segmentGranularity to "HOUR",use the timezone utc and not the local,there are so many file in realtime basePersist dir,and little file in localStorage.this below is the file list.
basePersist dir (in datasource dir, the same data source)
drwxr-xr-x 45 root root 4096 Nov 7 04:16 2015-11-06T08:00:00.000Z_2015-11-06T09:00:00.000Z
drwxr-xr-x 46 root root 4096 Nov 7 02:42 2015-11-06T09:00:00.000Z_2015-11-06T10:00:00.000Z
drwxr-xr-x 49 root root 4096 Nov 7 01:02 2015-11-06T10:00:00.000Z_2015-11-06T11:00:00.000Z
drwxr-xr-x 56 root root 4096 Nov 6 21:01 2015-11-06T12:00:00.000Z_2015-11-06T13:00:00.000Z
drwxr-xr-x 62 root root 4096 Nov 7 10:20 2015-11-06T13:00:00.000Z_2015-11-06T14:00:00.000Z
drwxr-xr-x 66 root root 4096 Nov 7 07:14 2015-11-06T14:00:00.000Z_2015-11-06T15:00:00.000Z
drwxr-xr-x 64 root root 4096 Nov 7 00:19 2015-11-06T15:00:00.000Z_2015-11-06T16:00:00.000Z
drwxr-xr-x 41 root root 4096 Nov 7 10:20 2015-11-06T16:00:00.000Z_2015-11-06T17:00:00.000Z
drwxr-xr-x 21 root root 4096 Nov 7 02:05 2015-11-06T17:00:00.000Z_2015-11-06T18:00:00.000Z
drwxr-xr-x 11 root root 4096 Nov 7 03:09 2015-11-06T18:00:00.000Z_2015-11-06T19:00:00.000Z
drwxr-xr-x 7 root root 4096 Nov 7 04:15 2015-11-06T19:00:00.000Z_2015-11-06T20:00:00.000Z
drwxr-xr-x 6 root root 4096 Nov 7 05:17 2015-11-06T20:00:00.000Z_2015-11-06T21:00:00.000Z
drwxr-xr-x 7 root root 4096 Nov 7 06:10 2015-11-06T21:00:00.000Z_2015-11-06T22:00:00.000Z
drwxr-xr-x 12 root root 4096 Nov 7 07:03 2015-11-06T22:00:00.000Z_2015-11-06T23:00:00.000Z
drwxr-xr-x 24 root root 4096 Nov 7 08:02 2015-11-06T23:00:00.000Z_2015-11-07T00:00:00.000Z
drwxr-xr-x 34 root root 4096 Nov 7 09:01 2015-11-07T00:00:00.000Z_2015-11-07T01:00:00.000Z
drwxr-xr-x 41 root root 4096 Nov 7 10:01 2015-11-07T01:00:00.000Z_2015-11-07T02:00:00.000Z
drwxr-xr-x 16 root root 4096 Nov 7 10:20 2015-11-07T02:00:00.000Z_2015-11-07T03:00:00.000Z
localStorage dir (in the same data source)
drwxr-xr-x 3 root root 4096 Nov 6 15:56 2015-11-06T05:00:00.000Z_2015-11-06T06:00:00.000Z
drwxr-xr-x 3 root root 4096 Nov 6 17:15 2015-11-06T06:00:00.000Z_2015-11-06T07:00:00.000Z
drwxr-xr-x 3 root root 4096 Nov 6 18:41 2015-11-06T07:00:00.000Z_2015-11-06T08:00:00.000Z
drwxr-xr-x 3 root root 4096 Nov 7 04:14 2015-11-06T08:00:00.000Z_2015-11-06T09:00:00.000Z
drwxr-xr-x 3 root root 4096 Nov 7 02:41 2015-11-06T09:00:00.000Z_2015-11-06T10:00:00.000Z
drwxr-xr-x 3 root root 4096 Nov 7 01:00 2015-11-06T10:00:00.000Z_2015-11-06T11:00:00.000Z
drwxr-xr-x 3 root root 4096 Nov 6 22:58 2015-11-06T11:00:00.000Z_2015-11-06T12:00:00.000Z
drwxr-xr-x 3 root root 4096 Nov 7 10:18 2015-11-06T13:00:00.000Z_2015-11-06T14:00:00.000Z
drwxr-xr-x 3 root root 4096 Nov 7 07:12 2015-11-06T14:00:00.000Z_2015-11-06T15:00:00.000Z
I can search the data well,is there something wrong with druid.
thank you!

[492066199]

if I restart the real time node,some of file in basePersist will be deleted.

[stale]

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