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    <p>Clearing the caches to measure performance is possible but very unwieldy.</p> <p>A very good measure for tracking achieved performance of tuning efforts is counting the number of read blocks during query execution. One of the easiest way to do this is using sqlplus with autotrace, like so:</p> <pre><code>set autotrace traceonly &lt;your query&gt; </code></pre> <p>outputs</p> <pre><code>... Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 1 consistent gets 0 physical reads 0 redo size 363 bytes sent via SQL*Net to client 364 bytes received via SQL*Net from client 4 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed </code></pre> <p>The number of blocks read, be it from cache or from disk, is <code>consistent gets</code>.</p> <p>Another way is running the query with increased statistics i.e. with the hint <code>gather_plan_statistics</code> and then looking at the query plan from the cursor cache:</p> <pre><code>auto autotrace off set serveroutput off &lt;your query with hint gather_plan_statistics&gt; select * from table(dbms_xplan.display_cursor(null,null,'typical allstats')); </code></pre> <p>The number of blocks read is output in column <code>buffers</code>.</p> <pre><code>--------------------------------------------------------------------------------------------------------------------- | Id | Operation | Name | Starts | E-Rows | Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers | --------------------------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 3 | | 1 (100)| | 3 |00:00:00.01 | 3 | | 1 | SORT AGGREGATE | | 3 | 1 | | | 3 |00:00:00.01 | 3 | | 2 | INDEX FULL SCAN| ABCDEF | 3 | 176 | 1 (0)| 00:00:01 | 528 |00:00:00.01 | 3 | --------------------------------------------------------------------------------------------------------------------- </code></pre>
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    1. POMy query runs faster the second time around, how do i stop that?
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    1. COinteresting but i created a composite index on columns that i am using in an analytic function, i want to see if and how effective this index is. Can i use what you describe to this effect? thx
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    2. COyes, every part of the query plan will show up with its associated cost. That includes your composite index if nothing unexpected happens. An unexpected thing could be that your index isn't used.
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