Support for roster versioning (EJAB-964)

Introduces two options for mod_roster and mod_roster_odbc:
- {versioning, true | false}   Enable or disable roster versioning on ejabberd.
- {store_current_id, true | false}   If true, the current roster version is stored on DB (internal or odbc). Otherwise it is calculated on the fly each time.

Performance:
Setting store_current_id to true should help in reducing the load for both ejabberd and the DB.

Details: 
If store_current_id is false,  the roster version is a hash of the entire roster. If store_current_id is true, the roster version is a hash, but of the current time
(this has to do with transactional semantics; we need to perform both the roster update and the version update on the same transaction, but we don't   
have the entire roster when we are changing a single item on DB. Loading it there requires significant changes to be introduced, so I opted for this simpler approach).

In either case, there is no difference for the clients, the roster version ID is opaque.

IMPORTANT:
mod_shared_roster is not compatible with the option 'store_current_id'.  Shared roster and roster versioning can be both enabled, but store_current_id MUST be set to false.

SVN Revision: 2428

1 files changed, 5 insertions, 0 deletions

diff --git a/src/odbc/pg.sql b/src/odbc/pg.sql
index 3cf3a0949..2273ad954 100644
--- a/src/odbc/pg.sql
+++ b/src/odbc/pg.sql
@@ -146,6 +146,11 @@ CREATE INDEX i_private_storage_username ON private_storage USING btree (username
 CREATE UNIQUE INDEX i_private_storage_username_namespace ON private_storage USING btree (username, namespace);
 
 
+CREATE TABLE roster_version (
+    username text PRIMARY KEY,
+    version text NOT NULL
+);
+
 -- To update from 0.9.8:
 -- CREATE SEQUENCE spool_seq_seq;
 -- ALTER TABLE spool ADD COLUMN seq integer;