Hi Will, On 12/17/15 10:17 AM, Will McCormick wrote: > I inherited a 9.1 replication environment > > Few basic questions that I can't find clear answers / clarifications for > if possible: > > 3 types of replication in 9.1 I've read about from the offical docs: > > 1) warm standby This is a standby which is applying WAL segments from the master (via recovery_command (log shipping) or streaming replication. > 2) hot standby Just like a warm standby but adds the ability to do read-only queries (and the master must know it is a hot standby). > 3) streaming replication Another way to deliver WAL segments from the master, but the advantage over recovery_command log shipping is that transactions are applied as soon as they happen on the master, rather than when a WAL segment is pushed from the master to the archive. > I'm using streaming replication I believe, the only indication I have > is that there is the primary_conninfo on the standby. Is this the only > indication? > > Is it possible to get if using streaming replication under normal > operations? > > /cp: cannot stat `/opt/postgres/9.1/archive/000000070000000F00000057': > No such file or directory/ > > /cp: cannot stat `/opt/postgres/9.1/archive/000000070000000F00000057': > No such file or directory/ > > /LOG: streaming replication successfully connected to primary/ > > /FATAL: could not receive data from WAL stream: FATAL: requested WAL > segment 000000070000000F00000057 has already been removed/ What this means is your stannby has been out-of-date for some time. The WAL segment it needs has been expired from both the archive (/opt/postgres/9.1/archive) and the master's pg_xlog directory. Your only option now (unless you can find to required WAL segments somewhere) is to do a new backup using pg_basebackup or some other mechanism to bring the standby up to date. > My understanding is that warm standby and hot standby do log shipping > and there is a greater window for transactions not to be send to the > standby because WAL XLOG must be filled. A hot or warm standby can be maintained with either log shipping or streaming replication. > Whereas Streaming replication basically sends at the transaction level? But yes, this is the advantage of streaming replication. I have written a tutorial that covers setting up a hot standby with or without streaming replication using pgBackRest: http://www.pgbackrest.org/user-guide.html#replication You can replace backup/restore/archive with other methods but the principal remains the same. The tutorial is for 9.4 but should work equally well with 9.1. -- -David david@xxxxxxxxxxxxx
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