naming of wal-archives - Mailing list pgsql-general

Hi all,

i am not sure whether  i have fully understood the implications of archiving wal-files and i have a few questions.

We currently keep a rather long backlog of wal-files, since we have a few hot-standbys over slow and unreliable lines that might fall back. So this is an extract from my current pg_xlog directory:

-rw-------  1 postgres postgres 16777216 Jan 29 16:03 000000010000008C0000008E

-rw-------  1 postgres postgres 16777216 Jan 29 16:32 000000010000008C0000008F

-rw-------  1 postgres postgres 16777216 Jan 29 16:35 000000010000008C00000090

-rw-------  1 postgres postgres 16777216 Jan  4 15:02 000000010000008C00000091

-rw-------  1 postgres postgres 16777216 Jan  4 15:02 000000010000008C00000092

As you can see it recycles existing files by using them with their exact name as they already exist (next file to be overwritten is the ..91-file). So far so good. I have, just a few minutes ago, set archive_mode to "on" and set an archive_command and restarted the server. Now files start appearing in the wal-archive directory. But i seem to have two "lines" of wal archives in my wal-storage directory, as the following extract shows:

My questions are as follows:

Why is postgres reusing the old files with the old names ? 

Is there a difference in the naming of wal-files if archive_mode = on compared to archive_mode = off ?

Does archive_mode = on combined with the use of a proper archive-command ensure that the naming of the wal-files will never collide with existing files ? If not, how do i prevent files from being overwritten when using an archive_command ? And how would i restore the needed file names for recovery if i decide to keep one base-backup und then a very long chain of wal-files ?

Is storing the output of pg_receivexlog equivalent to using archive_mode = on and using a proper archive_command ?

I have spent a more than a few hours on this, but am currently somewhat lost.

Thanks in advance,

Neil