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authoreinhverfr <einhverfr@4979c152-3d1c-0410-bac9-87ea11338e46>2006-09-30 15:01:08 +0000
committereinhverfr <einhverfr@4979c152-3d1c-0410-bac9-87ea11338e46>2006-09-30 15:01:08 +0000
commit4410a3d62f37dd01feba6aaaa9a1090248aa0d6a (patch)
tree6e21de4c258e463f14dbfeb2ab55cf88a09f5a27 /sql/README
parentf6f049eb28180b2e51f8dac70ef345ce889c847f (diff)
Fixed Pg-tables.sql, added scripts to configure replication
git-svn-id: https://ledger-smb.svn.sourceforge.net/svnroot/ledger-smb/trunk@174 4979c152-3d1c-0410-bac9-87ea11338e46
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+README
+------------
+$Id$
+Christopher Browne
+cbbrowne@gmail.com
+2006-09-29
+------------
+
+The script configure-replication.sh is intended to allow the gentle user
+to readily configure replication of the LedgerSMB database schema
+using the Slony-I replication system for PostgreSQL.
+
+For more general details about Slony-I, see <http://slony.info/>
+
+This script uses a number of environment variables to determine the
+shape of the configuration. In many cases, the defaults should be at
+least nearly OK...
+
+Global:
+ CLUSTER - Name of Slony-I cluster
+ NUMNODES - Number of nodes to set up
+
+ PGUSER - name of PostgreSQL superuser controlling replication
+ PGPORT - default port number
+ PGDATABASE - default database name
+
+For each node, there are also four parameters; for node 1:
+ DB1 - database to connect to
+ USER1 - superuser to connect as
+ PORT1 - port
+ HOST1 - host
+
+It is quite likely that DB*, USER*, and PORT* should be drawn from the
+default PGDATABASE, PGUSER, and PGPORT values above; that sort of
+uniformity is usually a good thing.
+
+In contrast, HOST* values should be set explicitly for HOST1, HOST2,
+..., as you don't get much benefit from the redundancy replication
+provides if all your databases are on the same server!
+
+slonik config files are generated in a temp directory under /tmp. The
+usage is thus:
+
+1. preamble.slonik is a "preamble" containing connection info used by
+ the other scripts.
+
+ Verify the info in this one closely; you may want to keep this
+ permanently to use with other maintenance you may want to do on the
+ cluster.
+
+2. create_set.slonik
+
+ This is the first script to run; it sets up the requested nodes as
+ being Slony-I nodes, adding in some Slony-I-specific config tables
+ and such.
+
+You can/should start slon processes any time after this step has run.
+
+3. store_paths.slonik
+
+ This is the second script to run; it indicates how the slons
+ should intercommunicate. It assumes that all slons can talk to
+ all nodes, which may not be a valid assumption in a
+ complexly-firewalled environment.
+
+4. create_set.slonik
+
+ This sets up the replication set consisting of the whole bunch of
+ tables and sequences that make up the LedgerSMB database schema.
+
+ When you run this script, all that happens is that triggers are
+ added on the origin node (node #1) that start collecting updates;
+ replication won't start until #5...
+
+ There are two assumptions in this script that could be invalidated
+ by circumstances:
+
+ 1. That all of the LedgerSMB tables and sequences have been
+ included.
+
+ This becomes invalid if new tables get added to LedgerSMB and
+ don't get added to the TABLES list in the generator script.
+
+ 2. That all tables have been defined with primary keys.
+
+ This *should* be the case soon if not already.
+
+5. subscribe_set_2.slonik
+
+ And 3, and 4, and 5, if you set the number of nodes higher...
+
+ This is the step that "fires up" replication.
+
+ The assumption that the script generator makes is that all the
+ subscriber nodes will want to subscribe directly to the origin
+ node. If you plan to have "sub-clusters", perhaps where there is
+ something of a "master" location at each data centre, you may
+ need to revise that.
+
+ The slon processes really ought to be running by the time you
+ attempt running this step. To do otherwise would be rather
+ foolish.
+
+Once all of these slonik scripts have been run, replication may be
+expected to continue to run as long as slons stay running.
+
+If you have an outage, where a database server or a server hosting
+slon processes falls over, and it's not so serious that a database
+gets mangled, then no big deal: Just restart the postmaster and
+restart slon processes, and replication should pick up.
+
+If something does get mangled, then actions get more complicated:
+
+1 - If the failure was of the "origin" database, then you probably want
+ to use FAIL OVER to shift the "master" role to another system.
+
+2 - If a subscriber failed, and other nodes were drawing data from it,
+ then you could submit SUBSCRIBE SET requests to point those other
+ nodes to some node that is "less mangled." That is not a real big
+ deal; note that this does NOT require that they get re-subscribed
+ from scratch; they can pick up (hopefully) whatever data they
+ missed and simply catch up by using a different data source.
+
+Once you have reacted to the loss by reconfiguring the surviving nodes
+to satisfy your needs, you may want to recreate the mangled node. See
+the Slony-I Administrative Guide for more details on how to do that.
+It is not overly profound; you need to drop out the mangled node, and
+recreate it anew, which is not all that different from setting up
+another subscriber.