Since the table is InnoDB
- Bulk Insert Buffer (bulk_insert_buffer_size) is no good for you because it handles bulk inserts for MyISAM tables only
DISABLE KEYS
/ ENABLE KEYS
only works for MyISAM. InnoDB handles secondary index processing in the system tablespace ibdata1.
You may have to resort to altering the InnoDB buffer protocol to handle only INSERTs :
Mysql load from infile stuck waiting on hard drive
Unless you plan to have store values in MLSNUMBER
bigger than 2147483647, you may want to consider making MLSNUMBER
an INT
(4 bytes) instead of BIGINT
(8 bytes) to save space on secondary index creation. If your values for MLSNUMBER
are less than 4294967296, maybe MLSNUMBER
should be INT UNSIGNED
.
Your indexes are fine for the two types of queries you mentioned.
This query will be satisfied by traversing the clustered index on the primary key...
[...] WHERE participant_id = x AND question_id = y AND given_answer_id = z;
...and this one is satisfied by the index on 'question_id':
[...] WHERE question_id = x;
The output of EXPLAIN SELECT
is not telling you what you think it is telling you, because the value shown in rows
is an estimate of the number of rows the server will need to consider, not the actual rows it will examine. For InnoDB
these are based on index statistics.
rows
The rows column indicates the number of rows MySQL believes it must examine to execute the query.
For InnoDB tables, this number is an estimate, and may not always be exact.
— http://dev.mysql.com/doc/refman/5.5/en/explain-output.html#explain_rows
The optimizer gathers information about different possible query plans, and chooses the one with the lowest cost. The information shown in EXPLAIN
is the information the optimizer gathered about the plan it selected.
When type
is ref
and key
is not NULL
, this means that the name listed in the key
column is the name of the index that the optimizer has chosen to use to find the desired rows, so your query plan looks exactly as it should.
Note, sometimes you will see Using index
in the Extra
column and a lot of people assume that this means an index is being used, or that no index is being used when that doesn't appear, but that's not correct, either. Using index
describes a special case called a "covering index" -- it does not indicate whether an index is being used to locate the rows of interest.
It's possible that running ANALYZE [LOCAL] TABLE
would cause the numbers in rows
shown by EXPLAIN
to differ, but this is a simple query and selecting this index is an obvious choice for the optimizer to make, so ANALYZE TABLE
is unlikely to make any actual difference in performance.
It is possible, however, that your overall performance might see some marginal improvement with an occasional OPTIMIZE [LOCAL] TABLE
, because you are not inserting rows in primary key order (as would be the case with an auto_increment
primary key)... but on large tables this can be time-consuming because it rebuilds a new copy of the table... but, again, I wouldn't expect any significant change.
Best Answer
You could use the additional module
pg_prewarm
. Has to be installed once per database. See:It can "prewarm" tables as well as indexes. To do it for your index:
Unless you get index-only scans (which you do not with the index at hand), you might want to prewarm the table as well:
There are more parameters to narrow down what and how to prewarm. Follow the links.
This is costly and the system might be better off using the cache for something else. If you know the exact query ahead of time and it's a
SELECT
without side effects, you might just run the query to "prewarm" relevant data pages of index and table.Aside, you might be better off rearranging PK and index like this:
Now, the PK index can give you index-only scans for the query at hand. Might make a substantial difference. See: