[Maria-developers] (no subject)
Hello Igor, I was reviewing histogram code. Not much feedback so far, but I thought I would let you know: == Code questions == Is middle_point_pos() a good functio nname? It was not apparent to me what it meant. For me, "middle point" is a point in the middle of a range, that is, a point equidistant from both ends. Maybe, "position_in_range" will be better? == Histogram storage questions == * What does hist_size column mean? I suppose, it is number of columns in the histogram? * Do we want to support only one kind of histogram? If not, maybe we should provision space for histogram type? * The histogram column is VARBINARY(255). Why set a hard limit of 255 bytes? Maybe, use a BLOB from the start? == A possible bug == I have a column with lots of NULLs: MariaDB [test]> select nulls_ratio from mysql.column_stats where table_name='one_k' and column_name='tnulls'; +-------------+ | nulls_ratio | +-------------+ | 0.9000 | +-------------+ 1 row in set (0.00 sec) The following query crashes in maria-10.0-mwl253 tree. AFAIU, Timour has fixed the crash in 10.0-mdev83 tree. With that tree, I get: MariaDB [test]> explain extended select * from one_k where tnulls is not null; +------+-------------+-------+------+---------------+------+---------+------+------+----------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +------+-------------+-------+------+---------------+------+---------+------+------+----------+-------------+ | 1 | SIMPLE | one_k | ALL | NULL | NULL | NULL | NULL | 969 | 100.00 | Using where | +------+-------------+-------+------+---------------+------+---------+------+------+----------+-------------+ 1 row in set, 1 warning (0.00 sec) Note that filtered=100%. It should be 10%. On Mon, Mar 25, 2013 at 11:48:30PM -0700, Igor Babaev wrote:
At file:///home/igor/maria/maria-10.0-mwl253/
------------------------------------------------------------ revno: 3502 revision-id: igor@askmonty.org-20130326064829-3x0g8p1g7nbptusd parent: igor@askmonty.org-20130311144424-cwqe1m70in3bora0 committer: Igor Babaev <igor@askmonty.org> branch nick: maria-10.0-mwl253 timestamp: Mon 2013-03-25 23:48:29 -0700 message: Added histogams for table columns.
BR Sergei -- Sergei Petrunia, Software Developer Monty Program AB, http://askmonty.org Blog: http://s.petrunia.net/blog
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Sergei Petrunia