MT#55307 SQL DB: kamailio.acc table, additional indexing

We have to concern slow selections like this:
"SELECT a.callid FROM acc a WHERE a.method = 'INVITE' GROUP BY a.callid LIMIT 0,200000;"

which can take procesisng time over 10 sec (as reported in the WF ticket).
As a simple solution, we can give an additional index to the 'acc' table:
KEY `method_callid_idx` (`method`,`callid`)

Which will give us an indexation on selecitons with the WHERE clause on 'method' column.

Without the index (explain of the selection):
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: a
         type: range
possible_keys: NULL
          key: callid_method_idx
      key_len: 817
          ref: NULL
         rows: 2
        Extra: Using where; Using index for group-by

With the index (explain of the selection):
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: a
         type: ref
possible_keys: method_callid_idx
          key: method_callid_idx
      key_len: 50
          ref: const
         rows: 1
        Extra: Using where; Using index

The newer index is not to be mixed with the previously existing one:
KEY `callid_method_idx` (`callid`,`method`)

Change-Id: Ie8a4ab102adb8788d9e273bd5a9edf1ddbb702bf

db_scripts/diff/15739.down

@@ -0,0 +1,4 @@
+SET sql_log_bin=0;
+USE kamailio;
+
+DROP INDEX method_callid_idx ON acc;

db_scripts/diff/15739.up

@@ -0,0 +1,4 @@
+SET sql_log_bin=0;
+USE kamailio;
+
+CREATE INDEX method_callid_idx ON acc (method,callid);