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Message Posted: Fri, 09 Jan 2004 @ 11:42:12 GMT


     
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Subj:   Explain Text - Synchronized Scanning
 
From:   Anomy Anom

<-- Anonymously Posted: Friday, January 09, 2004 06:36 -->

Hi,

When I did the explain "EXPLAIN SELECT * FROM TABLE_A", the second step of it was as below:

<<Next, we do an all-AMPs RETRIEVE step from Table_A by way of an all-rows scan with no residual conditions into Spool 1 (group_amps), which is built locally on the AMPs. The input table will not be cached in memory, but it is eligible for synchronized scanning. The result spool file will not be cached in memory. The size of Spool 1 is estimated with high confidence to be 78,436,942 rows. The estimated time for this step is 22 minutes and 17 seconds.>>


Can someone please throw light on the sentences:

a) "The input table will not be cached in memory, but it is eligible for synchronized scanning"

b) "The result spool file will not be cached in memory"


Also, is there an "asynchronized scanning" and "result spool file WILL BE cached in memory" ?. If yes, when would that happen and why ?


Thanks in advance.

Cheers



     
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