在MySQL中使用ENGINE作为MRG_MYISAM有什么优势

Question

I am doing a tracking site like google adwords. I am doing only modifications. In that site i have seen they are creating tables for each month and merging that table into one this is done for the tables which stores information about clicks and search details and the merged tables having crores of records.And for querying they have used only the merged table which is having crores of records. Is there any advantage of using tables like this?And the query is taking more than 10 minutes to execute.

Answer 1

Advantages are as follows, If you dont get the following advantages then do not use it.

Easily manage a set of log tables. For example, you can put data from different months into separate tables, compress some of them with myisampack, and then create a MERGE table to use them as one.

Obtain more speed. You can split a large read-only table based on some criteria, and then put individual tables on different disks. A MERGE table structured this way could be much faster than using a single large table.

Perform more efficient searches. If you know exactly what you are looking for, you can search in just one of the underlying tables for some queries and use a MERGE table for others. You can even have many different MERGE tables that use overlapping sets of tables.

Perform more efficient repairs. It is easier to repair individual smaller tables that are mapped to a MERGE table than to repair a single large table.

Instantly map many tables as one. A MERGE table need not maintain an index of its own because it uses the indexes of the individual tables. As a result, MERGE table collections are very fast to create or remap. (You must still specify the index definitions when you create a MERGE table, even though no indexes are created.)

If you have a set of tables from which you create a large table on demand, you can instead create a MERGE table from them on demand. This is much faster and saves a lot of disk space.

Exceed the file size limit for the operating system. Each MyISAM table is bound by this limit, but a collection of MyISAM tables is not.

You can create an alias or synonym for a MyISAM table by defining a MERGE table that maps to that single table. There should be no really notable performance impact from doing this (only a couple of indirect calls and memcpy() calls for each read).

You can read more about this on basic info link , advantages disadvantages link .

Answer 2

A MRG_MYISAM only works over MyISAM tables, which are, by themselves, not the first option for a table. You would normally go for InnoDB tables.

The MRG_MYISAM engine was invented before MySQL had support for views and for partitions. Range partitioning (eg partition per month) is most probably what you want.

Partitioning is transparent to the user in terms of queries, but nevertheless uses pruning so as to only read from selected partitions for a query, thus optimizing it.

I would recomment that you use InnoDB tables, and check out range partitioning . MRG_MYISAM and MyISAM are still in use. They could work out for you. It's just that MyISAM introduces so much trouble (no crash recovery, table level locking, more...) that it's many times out of the question.