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From:Dolan Antenucci Date:August 12 2013 5:26pm
Subject:MyISAM index missing rows
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Hi Everyone,

I have a MyISAM table with 25 billion rows (structure: <id1 int, id2 int,
score float>), and after I create an index on id1, certain rows can no
longer be found.

I've posted a detailed summary of my problem at dba.stackexchange.com, but
haven't had success with finding a solution thus far.  Here's the URL to
that post:
http://dba.stackexchange.com/questions/47906/mysql-myisam-index-causes-query-to-match-no-rows-indexes-disabled-rows-match

As that post describes, one oddity is with an EXPLAIN I run on the same
query with indexes enabled vs. disabled. When disabled, "rows" = 25
billion; when enabled, "rows" = 170 million.  Based on this, I'm wondering
if some restriction is causing only 170 million rows to index. (Of course,
I could be completely misinterpreting this EXPLAIN result).

Here is my server version: 5.5.31-0ubuntu0.12.04.2 (Ubuntu), which should
also be 64-bit (i've verified by running "file /usr/sbin/mysqld" (says "ELF
64 bit..")

Any help is greatly appreciated!  Just let me know if you need more details

Sincerely,

Dolan Antenucci

Thread
MyISAM index missing rowsDolan Antenucci12 Aug
  • RE: MyISAM index missing rowsRick James12 Aug