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, 16 insertions, 1 deletions

diff --git a/src/odbc/odbc_queries.erl b/src/odbc/odbc_queries.erl
index ef1f59218..f70b8fb35 100644
--- a/src/odbc/odbc_queries.erl
+++ b/src/odbc/odbc_queries.erl
@@ -78,7 +78,9 @@
 	 set_vcard/26,
 	 get_vcard/2,
 	 escape/1,
-	 count_records_where/3]).
+	 count_records_where/3,
+	 get_roster_version/2,
+	 set_roster_version/2]).
 
 %% We have only two compile time options for db queries:
 %-define(generic, true).
@@ -555,6 +557,13 @@ count_records_where(LServer, Table, WhereClause) ->
     ejabberd_odbc:sql_query(
       LServer,
       ["select count(*) from ", Table, " ", WhereClause, ";"]).
+
+
+get_roster_version(LServer, LUser) ->
+	ejabberd_odbc:sql_query(LServer,
+		["select version from roster_version where username = '", LUser, "'"]).
+set_roster_version(LUser, Version) ->
+	update_t("roster_version", ["username", "version"], [LUser, Version], ["username = '", LUser, "'"]).
 -endif.
 
 %% -----------------
@@ -791,4 +800,10 @@ count_records_where(LServer, Table, WhereClause) ->
     ejabberd_odbc:sql_query(
       LServer,
       ["select count(*) from ", Table, " ", WhereClause, " with (nolock)"]).
+
+get_roster_version(LServer, LUser) ->
+	ejabberd_odbc:sql_query(LServer, 
+		["select version from dbo.roster_version where username = '", LUser, "'"]).
+set_roster_version(LUser, Version) ->
+	update_t("dbo.roster_version", ["username", "version"], [LUser, Version], ["username = '", LUser, "'"]).
 -endif.