[PERFORM] Poor Query

[Pallav Kalva]

Hi Everybody,
    I have a performance problem with this query , it takes lot of time 
on the production database. is there a way to improve it ? i do vacuumdb 
on this database and do anlyze on the users table separately daily

select userID, fname, lname, email, phone, dateEntered, dateCanceled,
dateSuspended, billAmount, billDate, dateBilled, datePaid, '?' as searches
from Users u
where 1=1 AND exists (select userID
           from bankaccount ba
           where ba.bankaccountID = u.bankaccountID
           and   ba.accountnumber = '12345678')
AND exists (select userID
        from bankaccount ba
        where ba.bankaccountID = u.bankaccountID
        and ba.routingNumber = '12345678')
order by UserID desc
limit 500
                                            QUERY PLAN
-----------------------------------------------------------------------------------------------------
Limit  (cost=0.00..12752.61 rows=500 width=120)
  ->  Index Scan Backward using users_pkey on users u  
(cost=0.00..2460462.79 rows=96469 width=120)
        Filter: ((subplan) AND (subplan))
        SubPlan
          ->  Index Scan using bankaccount_pkey on bankaccount ba  
(cost=0.00..3.07 rows=1 width=0)
                Index Cond: (bankaccountid = $1)
                Filter: (routingnumber = '12345678'::text)
          ->  Index Scan using bankaccount_pkey on bankaccount ba  
(cost=0.00..3.07 rows=1 width=0)
                Index Cond: (bankaccountid = $1)
                Filter: (accountnumber = '12345678'::text)

I tried changing it but it still takes lot of time
select userID, fname, lname, email, phone, dateEntered, dateCanceled,
dateSuspended, billAmount, billDate, dateBilled, datePaid, '?' as searches
from Users u
where 1=1 AND exists (select userID
           from bankaccount ba
           where ba.bankaccountID = u.bankaccountID
           and   ba.accountnumber = '12345678'
                  and ba.routingNumber = '12345678')
order by UserID desc
limit 500
                                             QUERY PLAN
-------------------------------------------------------------------------------------------------------
Limit  (cost=0.00..3309.62 rows=500 width=120)
  ->  Index Scan Backward using users_pkey on users u  
(cost=0.00..1277101.86 rows=192938 width=120)
        Filter: (subplan)
        SubPlan
          ->  Index Scan using bankaccount_pkey on bankaccount ba  
(cost=0.00..3.07 rows=1 width=0)
                Index Cond: (bankaccountid = $1)
                Filter: ((accountnumber = '12345678'::text) AND 
(routingnumber = '12345678'::text))

  the users_pkey index on the primary key userid is on users table. it 
seems to be using index but it still takes lot of time.
 here is the output from the pg_class for the users and bankaccount 
table . Table doesnt have lot of records but this query take anywhere 
from 3 to 5 min to run which is really bad for us. Can we improve the 
performance on this query ?

relname | relpages | reltuples
---------+----------+-----------
users   |    39967 |    385875
bankaccount |      242 |     16453
Thanks!
Pallav


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