archive_command and restore_command describe how to ship WAL files to/from an archive.
When there is nothing to ship, we delay sending WAL files. When no WAL files, the standby has no information at all. To provide some form of keepalive on quiet systems the archive_keepalive_command provides a generic hook to implement keepalives. This is implemented as a separate command to avoid storing keepalive messages in the archive, or at least allow overwrites using a single filename like "keepalive". Examples archive_keepalive_command = 'arch_cmd keepalive' # sends a file called "keepalive" to archive, overwrites allowed archive_keepalive_command = 'arch_cmd %f.%t.keepalive #sends a file like 000000010000000AB00000000FE.20111216143517.keepalive If there is no WAL file to send, then we send a keepalive file instead. Keepalive is a small file that contains same contents as a streaming keepalive message (re: other patch on that). If no WAL file is available and we are attempting to restore in standby_mode, then we execute restore_keepalive_command to see if a keepalive file is available. Checks for a file in the specific keepalive format and then uses that to update last received info from master. e.g. restore_keepalive_command = 'restore_cmd keepalive' # gets a file called "keepalive" to archive, overwrites allowed Additions/changes? -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers