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Re: Why is ORDER BY ASC is slow but ORDER DESC is fast ? and how can i fix it ?
Posted by: Rick James
Date: October 05, 2015 10:38AM

Notice that the 'key' it picked was targeted at
ORDER BY comments_count
For ASC vs DESC, probably the desired (re: WHERE) rows were at one end of the table instead of the other. That would explain ASC and DESC having distinctly different times. The Handler numbers confirm it:
| Handler_read_next | 6799069 | versus
| Handler_read_prev | 25635 |

This is a drawback of
WHERE ... ORDER BY ...
and having both
INDEX(tailored for WHERE)
INDEX(tailored for ORDER BY)
The Optimizer tries both, but does not have adequate statistics to always make the right choice.

I dislike "index hints", but this might be warranted in your case:
FROM content IGNORE INDEX(comments_count)

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Why is ORDER BY ASC is slow but ORDER DESC is fast ? and how can i fix it ?
2519
Ronald Brown
October 03, 2015 12:47AM
Re: Why is ORDER BY ASC is slow but ORDER DESC is fast ? and how can i fix it ?
1395
Rick James
October 03, 2015 08:01PM
Re: Why is ORDER BY ASC is slow but ORDER DESC is fast ? and how can i fix it ?
1396
Ronald Brown
October 03, 2015 08:34PM
Re: Why is ORDER BY ASC is slow but ORDER DESC is fast ? and how can i fix it ?
1191
Rick James
October 05, 2015 10:38AM
Re: Why is ORDER BY ASC is slow but ORDER DESC is fast ? and how can i fix it ?
1139
Rick James
October 05, 2015 10:41AM
Re: Why is ORDER BY ASC is slow but ORDER DESC is fast ? and how can i fix it ?
1118
Ronald Brown
October 05, 2015 10:50AM
Re: Why is ORDER BY ASC is slow but ORDER DESC is fast ? and how can i fix it ?
1046
Ronald Brown
October 04, 2015 08:28PM
Re: Why is ORDER BY ASC is slow but ORDER DESC is fast ? and how can i fix it ?
1095
Ronald Brown
October 05, 2015 12:26PM
Re: Why is ORDER BY ASC is slow but ORDER DESC is fast ? and how can i fix it ?
1184
Rick James
October 06, 2015 11:00AM
Re: Why is ORDER BY ASC is slow but ORDER DESC is fast ? and how can i fix it ?
2778
Ronald Brown
October 06, 2015 11:50PM
Re: Why is ORDER BY ASC is slow but ORDER DESC is fast ? and how can i fix it ?
1140
Rick James
October 07, 2015 08:12PM
Re: Why is ORDER BY ASC is slow but ORDER DESC is fast ? and how can i fix it ?
1091
Ronald Brown
October 08, 2015 11:17PM
Re: Why is ORDER BY ASC is slow but ORDER DESC is fast ? and how can i fix it ?
1169
Rick James
October 09, 2015 10:34PM


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