inner join in mysql (to-many connections) - mysql

Question

SELECT
a.cdrID as cdrID,
a.userName as userName,
a.callingStationID as callingStationID,
a.orgClientAccountID as orgClientAccountID,
a.terClientAccountID as terClientAccountID,
a.calledStationID as calledStationID,
a.setupTime as setupTime,
a.connectTime as connectTime,
a.disconnectTime as disconnectTime,
a.orgDestCode as orgDestCode,
a.orgBilledDuration as orgBilledDuration,
a.orgBilledAmount as orgBilledAmount,
a.terDestCode as terDestCode,
a.terBilledDuration as terBilledDuration,
a.terBilledAmount as terBilledAmount,
a.orgRateID as orgRateID,
a.terRateID as terRateID,
b.dtDestName as orgDestName,
c.dtDestName as terDestName,
d.clCustomerID as terClientName,
1 as cdrwsid,
cast((e.crFlatRate*a.orgBilledAmount)as decimal(10,4)) as cdrsale,
cast((f.crFlatRate*a.terBilledAmount)as decimal(10,4)) as cdrpurchase,
cast(((e.crFlatRate*a.orgBilledAmount)-(f.crFlatRate*a.terBilledAmount))as decimal(10,4)) as cdrprofit
FROM Successful.vbSuccessfulCDR_508 a
inner join iTelBilling.vbDestination b on a.orgDestCode=b.dtDestCode
inner join iTelBilling.vbDestination c on a.terDestCode=c.dtDestCode
inner join iTelBilling.vbClient d on a.terClientAccountID=d.clAccountID
inner join iTelBilling.vbCallRate e on a.orgRateID=e.crCallRateID
inner join iTelBilling.vbCallRate f on a.terRateID=f.crCallRateID
where setupTime between '1317761709564' and '1317804909564' and a.terBilledDuration!=0
I have problem with this query some time this query runs fine some time it got hanged on server and some time it through error to-many connections. Can any one tell me what to do.

Answer 1

The problem sounds like this query is running very long; This can be due to the fact, that you need to have a look at the indexes that the query uses. To get an overview (and perhaps optimize your indexes and pks) use the command:
> EXPLAIN SELECT
a.cdrID as cdrID,
a.userName as userName,
...
Another reason can be, that there are deadlock-situations or situations, where the query is running very long since a table is locked. If this happens, other users that execute that query (I assume you are using it in an webserver-context) are building up a "waiting row". Each user that executes this query (which is waiting) needs a connection of its own. If this happens, your server is running out of concurrent connections in a short time.
This can be solved in two ways:
1) Make sure your query has more performance (check the pks and indexes)
2) Increase your concurrent connections settings in your SQL-server:
This can be done by setting the following value to 200 connections (for example) in your my.cnf
max_connections = 200
3) Optimize your mySQL. Make sure your querycache, key-buffer, ... are set to a fitting value. Further informations on mySQL-Performance tuning you will find here.

Answer 2

It might be that the engine is trying to use your SMALLER lookup tables for performing the join instead of your PRIMARY table of CRD (Call Data Records), like phone system billing. You are trying to get proper origination / destination billing codes and rates. Sometimes MySQL will try to think for you by using the smaller tables first.
Ensure you have an index on your Successful table on the "setupTime". In addition, add "STRAIGHT_JOIN" clause to the top
SELECT STRAIGHT_JOIN ... rest of query.
This tells MySQL to process based on the tables you have ordered in that order. It appears the joins to your destination, client and call rate tables WOULD have the corresponding index on their join keys respectively... if not create them.