MySql complicated join performance issue - mysql

Question

Please consider the following query
SELECT * FROM PC_SMS_OUTBOUND_MESSAGE AS OM
JOIN MM_TEXTOUT_SERVICE AS TOS ON TOS.TEXTOUT_SERVICE_ID = OM.SERVICE_ID
JOIN PC_SERVICE_NUMBER AS SN ON OM.TO_SERVICE_NUMBER_ID = SN.SERVICE_NUMBER_ID
JOIN PC_SUBSCRIBER AS SUB ON SUB.SERVICE_NUMBER_ID = SN.SERVICE_NUMBER_ID
JOIN MM_CONTACT CON ON CON.SUBSCRIBER_ID = SUB.SUBSCRIBER_ID
--AND CON.MM_CLIENT_ID = 1
AND OM.CLIENT_ID= 1
AND OM.CREATED>='2013-05-08 11:47:53' AND OM.CREATED<='2014-05-08 11:47:53'
ORDER BY OM.SMS_OUTBOUND_MESSAGE_ID DESC LIMIT 50
To get the dataset I require I need to filter on the (commented out) CONTACTS client_id as well as the OUTBOUND_MESSAGES client_id but this is what changes the performance from milliseconds to tens of minutes.
Execution plan without "AND CON.MM_CLIENT_ID = 1":
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE OM index FK4E518EAA19F2EA2B,SERVICEID_IDX,CREATED_IDX,CLIENTID_IDX,CL_CR_ST_IDX,CL_CR_STYPE_ST_IDX,SID_TOSN_CL_CREATED_IDX PRIMARY 8 NULL 6741 3732.00 Using where
1 SIMPLE SUB ref PRIMARY,FKA1845E3459A7AEF FKA1845E3459A7AEF 9 mmlive.OM.TO_SERVICE_NUMBER_ID 1 100.00 Using where
1 SIMPLE SN eq_ref PRIMARY PRIMARY 8 mmlive.OM.TO_SERVICE_NUMBER_ID 1 100.00 Using where
1 SIMPLE CON ref FK2BEC061CA525D30,SUB_CL_IDX FK2BEC061CA525D30 8 mmlive.SUB.SUBSCRIBER_ID 1 100.00
1 SIMPLE TOS eq_ref PRIMARY,FKDB3DF298AB3EF4E2 PRIMARY 8 mmlive.OM.SERVICE_ID 1 100.00
Execution plan with "AND CON.MM_CLIENT_ID = 1":
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE CON ref FK2BEC061CA525D30,FK2BEC06134399E2A,SUB_CL_IDX FK2BEC06134399E2A 8 const 18306 100.00 Using temporary; Using filesort
1 SIMPLE SUB eq_ref PRIMARY,FKA1845E3459A7AEF PRIMARY 8 mmlive.CON.SUBSCRIBER_ID 1 100.00
1 SIMPLE OM ref FK4E518EAA19F2EA2B,SERVICEID_IDX,CREATED_IDX,CLIENTID_IDX,CL_CR_ST_IDX,CL_CR_STYPE_ST_IDX,SID_TOSN_CL_CREATED_IDX FK4E518EAA19F2EA2B 9 mmlive.SUB.SERVICE_NUMBER_ID 3 100.00 Using where
1 SIMPLE SN eq_ref PRIMARY PRIMARY 8 mmlive.SUB.SERVICE_NUMBER_ID 1 100.00 Using where
1 SIMPLE TOS eq_ref PRIMARY,FKDB3DF298AB3EF4E2 PRIMARY 8 mmlive.OM.SERVICE_ID 1 100.00
Any suggestions on how to format the above to make it a little easier on the eye would be good.
ID fields are primary keys.
There are indexes on all joining columns.

Answer 1

You may be able to fix this problem by using a subquery:
JOIN (SELECT C.* FROM CONTACTS C WHERE C.USER_ID = 1) ON C.SUBSCRIBER_ID = SUB.ID
This will materialize the matching rows, which could have downstream effects on the query plan.
If this doesn't work, then edit your query and add:
The explain plans for both queries.
The indexes available on the table.
EDIT:
Can you try creating a composite index:
PC_SMS_OUTBOUND_MESSAGE(CLIENT_ID, CREATED, SERVICE_ID, TO_ SERVICE_ID, SMS_OUTBOUND_MESSAGE_ID);
This may change both query plans to start on the OM table with the appropriate filtering, hopefully making the results stable and good.

Answer 2

I've solved the riddle! For my case anyway so I'll share.
This all came down to the join order changing once I added that extra clause, which you can clearly see in the execution plan. When the query is fast, the Outbound Messages are at the top of the plan but when slow (after adding the clause), the Contacts table is at the top.
I think this means that the Outbound Messages index can no longer be utilised for the sorting which causes the dreaded;
"Using temporary; Using filesort"
By simply adding STRAIGHT_JOIN keyword directly after the select I could force the execution plan to join in the order denoted directly by the query.
Happy for anyone with a more intimate knowledge of this field to contradict any of the above in terms of what is actually happening but it definitely worked.