Why is this MySQL FULLTEXT query returning 0 rows when matching rows are present?

Posted by Don MacAskill on Server Fault See other posts from Server Fault or by Don MacAskill
Published on 2011-03-04T23:19:11Z Indexed on 2011/03/04 23:26 UTC
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mysql

I have a MySQL table with >200M rows which has a FULLTEXT index on two columns (Title,Body).

When I do a simple FULLTEXT query in the default NATURAL LANGUAGE mode for some popular results (they'd return 2M+ rows), I'm getting zero rows back:

SELECT COUNT(*) FROM itemsearch WHERE MATCH (Title, Body) AGAINST ('fubar');

But when I do a FULLTEXT query in BOOLEAN mode, I can see the rows in question do exist (I get 2M+ back, depending):

SELECT COUNT(*) FROM itemsearch WHERE MATCH (Title, Body) AGAINST ('+fubar' IN BOOLEAN MODE);

I have some queries which return ~500K rows which are working fine in either mode, so if it's result size related, it seems to crop up somewhere between 500K and a little north of 2M.

I've tried playing with the various buffer size variables, to no avail. It's clearly not the 50% threshold, since we're not getting 100M rows back for any result.

Any ideas?

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