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Bookmark Operator

  • July 19, 2007 at 3:58 am

    #117949

    Hi All,

    I am pretty much a novice when it comes to query tuning so I would like some advice. I have a long running query which I have broken down to try to establish where the problems lie.

    I have issued a query against 1 large table (28 million rows!)  with 3 where clauses. I have viewed the estimated execution plan and a Bookmark Lookup is taking up 69% of the cost to the batch.

    What does this operator do and what can I look at to improve the performance of this query?

    I am only carrying out a count(*) and the query returns 32k rows anything between 30 secs and 3 mins. This is probably down to the activity on the server.

    I would appreciate your views?

    Thanks.

  • July 19, 2007 at 6:22 am

    #720713

    HI Adam,

    Could you please post the query you are running.

    I'll then have a look at this and try and point you in the correct direction.

    thanks

    Chris

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  • July 19, 2007 at 6:25 am

    #720717

    A bookmark lookup is when the query uses a non-clustered index to finds rows matching and then uses a clustered index to find the row in the table.

    If you are doing just a count(*) then I suspect that one of the columns in the where clause is not in the index. If you add this column, the index becomes a covered index and the optimiser can resolve the count(*) just from the index without having to touch the table.  It should be much faster.

    J

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