On 11/20/14, Adrian Klaver <adrian.klaver@xxxxxxxxxxx> wrote: > On 11/20/2014 12:30 PM, zach cruise wrote: >>> >>> For more info see: >>> >>> http://www.postgresql.org/docs/9.3/interactive/continuous-archiving.html >> to be clear- i change my 2 VMs setup {"1. master (dev) - 2. slave >> (prod) setup"} to 3 VMs {"1. master (dev) - 2. slave (prod) setup - 3. >> archive (wal)"}. >> >> but what do i gain? > > Extra protection against failure, maybe. > > So: > > ---> WAL Archive --- > | | > | Streaming | > master --- --------------------> slave > > If the direct link between the master and slave goes down, the slave can > still get WALs from the archive. If the archive machine goes down you > still have the direct link. If you take the slave down the master can > still push WALs to the archive. This assumes the 'machines' are actually > separated and connecting through different networks. You say you are > using VMs, but not where they are running. If they are all running on > the same machine running through the same network link then you really > do not have protection against network issues. The same if the host > machine goes down. This is one of those pen and paper times, when you > sketch out the arrangement and start doing what ifs. master, slave and archive can be 3 separate VMs on 1 host, with their clones on 2nd and 3rd hosts. a follow-up question on WAL recycling: ("When WAL archiving is being done, the log segments must be archived before being recycled or removed" from http://www.postgresql.org/docs/9.3/static/wal-configuration.html) say streaming is off- * if both master and archive are down, slave is still up and running. yes? * if master writes data when archive is down, it will copy over to slave when archive is back up. yes? * but if WAL is recycled before archive is back up, it will not copy over to slave. yes? see my concern with a separate archive is if archive is down and master gets stuck retrying to push the same segment again and again, there may be a problem in recovery when archive is back up. no? -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
