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SHOW CREATE TABLE suddenly slow on InnoDB?

+1 vote
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I'm trying to figure out how InnoDB executes a SHOW CREATE TABLE query so I can figure out what could possibly have made them suddenly slow down?

mysql> SHOW CREATE TABLE my_table;
...
1 row in set (37.48 sec)

We tend to execute many of these statements concurrently, but it's never been a problem until recently. I upgraded the IO subsystem, and our statistics indicate that it's not maxing out IO (at least IOPS).

posted Mar 17, 2014 by Jagan Mishra

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1 Answer

+1 vote

What version are you using? My immediate thought is to check if innodb_stats_on_metadata is off. If it is on, switch off and check your timings again.

answer Mar 17, 2014 by Amit Mishra
I'm on 5.5.27.  Just flipped that setting off and getting the same results. It pretty clearly seems to be InnoDB: If I create a HEAP table, I don't get this behavior.

I have (and always have had) innodb_file_per_table enabled, but my tablespace file is still gigantic (56GB)?
My guess is that it could be contention trying to open the table. i.e. when you run into this issue and run SHOW PROCESSLIST, does it show any threads waiting in state “Opening tables”?
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Below table contains billion of rows,

CREATE TABLE `Sample1` (
  `c1` bigint(20) NOT NULL AUTO_INCREMENT,
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  `c3` tinyint(4) DEFAULT NULL,
  `c4` tinyint(4) DEFAULT NULL,
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  KEY `varchar_c3_time_idx` (`c2`,`c3`,`Time`),
  KEY `varchar_c4_time_idx` (`c2`,`c4`,`Time`),
  KEY `varchar_c3_c4_time_idx` (`c2`,'c3', `c4`,`Time`),
) ENGINE=InnoDB AUTO_INCREMENT=10093495 DEFAULT CHARSET=utf8

Four multi column index created because having below conditions in where

1) c2 and time
2) c2 and c3 and time
3) c2 and c4 and time
4) c2 and c3 and c4 and time

Cardinality wise c2, c3 and c4 are very low. (ex: Out of one million c2, c3 and c4 have 50 unique column in each)

Column time contains mostly unique fields.

Select, insert and update happened frequently.

Tables has 5 indexing fields(4 multi column). Due to this, 1) Insert and update on index fields become costlier. 2) As the table keep on growing (Nearly one billion rows), Index size also increase more rapidly.

Kindly suggest good approach in mysql to solve this use case.

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SELECT TABLE_SCHEMA,TABLE_NAME
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After that, I have seen that there are 49 fragmented tables. With one table, I have executed "optimize table table_name;" and "analyze table table_name;". The result is the same, the table continuous fragmented.

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