Re: what does "index map: N" mean?

Baron Schwartz wrote:
> Jay Pipes wrote:

>> This is very interesting.  Sergey, is this engine-agnostic?  I know 
>> that Falcon has sparse bitmap indexing (already?) but I did not know 
>> if other engines support the concept (if not, are we "emulating" it in 
>> the optimizer?)
>>
>> Baron, which engine are you testing against?

given what is documented on

   http://dev.mysql.com/doc/refman/5.0/en/explain.html

it looks as if it is just showing a column bitmap for the utilized index:

   # range checked for each record (index map: N)

   MySQL found no good index to use, but found that some of indexes might    be used after column values from preceding tables are known. For each    row combination in the preceding tables, MySQL checks whether it is    possible to use a range or index_merge access method to retrieve rows.    This is not very fast, but is faster than performing a join with no    index at all. The applicability criteria are as described in Section 6.2.5,    “Range Optimization”, and Section 6.2.6, “Index Merge Optimization”,    with the exception that all column values for the preceding table are    known and considered to be constants.

looks as if the documentation needs to go into more detail here

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Hartmut Holzgraefe, Senior Support Engineer                            .
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