One concern I have about these trigger based replication systems is that I fear it may ping the slave for each and every DML statement separately in time and in a transaction. My slave will literally be 1400 miles away and all replication communications will be over the net. If I have a transaction which has 1000 DML statements in it, is this thing going to update the slave 1000 times separately over the net ? (I may not live long enough to see it finish) Or will it be smart enough to wait until I "commit" then send over a single bundle of 1000 DML? The time diff will be more than significant.
Thanks for all the great input on this! -----Original Message----- From: pgsql-general-ow...@postgresql.org [mailto:pgsql-general-ow...@postgresql.org] On Behalf Of Greg Sabino Mullane Sent: Thursday, December 17, 2009 11:58 AM To: pgsql-general@postgresql.org Subject: Re: [GENERAL] Justifying a PG over MySQL approach to a project -----BEGIN PGP SIGNED MESSAGE----- Hash: RIPEMD160 > How difficult is it to switch the master's hat from one DB instance > to another? Let's say the master in a master-slave scenario goes > down but the slave is fine. Can I designate the slave as being the > new master, use it for read/write, and then just call the broken > master the new slave once it comes back to life (something like that)? Sure. Bucardo slaves are not changed at all, so they are already read/write and don't need anything special done to "unslave" them. One possible way to handle the scenario is: Assuming three servers: * A (master) sends changes to B, receives read/write queries * B (slave) has transaction_read_only set to true, receives read queries * C has the Bucardo database and daemon Box A goes down suddenly. * Stop Bucardo on box C * Flip the boxes around in the bucardo.db table * Do a 'bucardo_ctl validate sync all' (This will create the needed triggers on B) * Set B's transaction_read_only to false * Point your apps at B instead of A for read/write queries When A comes back up: * DROP SCHEMA bucardo CASCADE; (drops all triggers) * Set transaction_read_only to true * Start Bucardo on C * Once caught up, point read-only queries to A If you are in a rush, you point things to B immediately after A fails, but you'll have to recopy the entire table data to the slave, as the triggers won't be in place yet. - -- Greg Sabino Mullane g...@turnstep.com End Point Corporation http://www.endpoint.com/ PGP Key: 0x14964AC8 200912171153 http://biglumber.com/x/web?pk=2529DF6AB8F79407E94445B4BC9B906714964AC8 -----BEGIN PGP SIGNATURE----- iEYEAREDAAYFAksqYqUACgkQvJuQZxSWSsjZtQCfTwbI3f9W0z+82IU7lL+2LwNK aUYAnj3AMjRDOeFIuHDee4JJemneArie =75Ho -----END PGP SIGNATURE----- -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
