Toru,
I am having trouble locating the specific docs at this time, I will
look deeper tonight.
Wether this applies to your specific range optimization.. I am not sure.
But...
I believe that both the MySQL memory storage engine , and the
ndbcluster storage engine perform some tricks to force the optimizer
to favor one type of access over another.
memory, because the index and the data are in memory vs the usual
analysis of index in memory, data on disk.
Cluster..
For similar reasons.. plus additional details.
I will see if I can find the docs.
--
Tom
On 22 Mar 2010, at 13:05, Toru Maesaka wrote:
Hi!
Would it make sense to have an engine-level option to tell the
optimizer to prioritize index use at all times? Something along the
line of HA_PRIORITIZE_INDEX.
I'm saying this because the relationship between
Cursor::records_in_range() and HA_READ_RANGE seems important to
effectively perform range scans at the moment. I tried purposely
returning a constant small cost factor in records_in_range() but it
seems that the range search will fail if the number of estimated rows
(in my case a total lie) is significantly smaller than the number of
actual rows in the table. If I don't set, HA_READ_RANGE then it seems
Drizzle will resort to a table scan (despite knowing that
'possible_keys' exist in EXPLAIN).
Preferably, I don't want to count through the number of rows in a
range for the optimizer on every simple query. Although... a
completely dishonest implementation of records_in_range() would dirty
the EXPLAIN statement result. So there is definitely a downside to
what I was experimenting with.
It would be great to hear what you all think :)
- Toru
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Tom Hanlon
[email protected]
Cloudera Certified Hadoop Developer
Certified MySQL DBA
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