Michael McTernan wrote:
Hi,
SELECT COUNT(*) for InnoDB tables is a know problem... The table
handler (for InnoDB) has to do a table scan to count all rows... This
particular case is optimized with MyISAM ...
Sure. But why is the tablescan ~100 times faster for the table without the
BLOB column?
Well, two possible explanations... BLOBS are either stored in a
separate area thus forcing MySQL to perform an extra seek to retrieve
the full row or the table scan takes a lot more time to execute because
of the BLOB data you have to retrieve... Reading 100000 rows of 1K is
way faster than retrieving 100000 rows of 800K! By your result, I am
assuming that your table with the BLOB is 100 times bigger than the one
without it...
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