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13.5.6 Maria Design Notes »
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13.5.5. Maria Statement Concurrency

The concurrency of statement execution on tables is handled differently in Maria depending on whether you are using non-transactional or transactional tables.

For non-transactional tables, the rules are identical to MyISAM:

  • SELECT

    All issued SELECT's are running concurrently. While a SELECT is running, all writers (INSERT, DELETE, UPDATE) are blocked from using any of the used tables (i.e., they wait for the table to be free before continuing) . The only exception is that one INSERT CONCURRENT can be run on each table that doesn't have any deleted rows.

  • UPDATE

    Only one UPDATE statement can run at the same time on each table. While the UPDATE is running all other threads are blocked from using this table.

  • DELETE

    Only one DELETE statement can run at the same time on each table. While the DELETE is running all other threads are blocked from using this table.

  • INSERT

    If INSERT CONCURRENT is used, and there are no deleted rows in the table, only one INSERT CONCURRENT statement can run at the same time on each table. While the INSERT CONCURRENT is running all other writer threads are blocked for using this table. Any number of SELECT statements can use this table.

    If normal INSERT is used or if there are deleted rows in the table, only one INSERT statement can run at the same time on the table. While the INSERT is running all SELECT, INSERT, DELETE and UPDATE are blocked from using this table.

  • CREATE or DROP

    CREATE's on different tables can be run concurrently. On the same table, first creator wins. DROP waits until all statements using the tables are completed, after which the table is dropped.

When using transactional tables:

  • SELECT

    All issued SELECT's are running concurrently. While a SELECT is running, all writers (INSERT, DELETE, UPDATE) are blocked from using any of the used tables (ie, they wait for the table to be free before continuing).

  • UPDATE

    Only one UPDATE statement can run at the same time on each table. While the UPDATE is running all other threads are blocked from using this table.

  • DELETE

    Only one DELETE statement can run at the same time on each table. While the DELETE is running all other threads are blocked from using this table.

  • INSERT

    Only one INSERT statement can run at the same time on the table. While the INSERT is running all SELECT, INSERT, DELETE and UPDATE are blocked from using this table.

  • CREATE or DROP

    CREATE's on different tables can be run concurrently. On the same table, first creator wins. DROP waits until all statements using the tables are completed, after which the table is dropped.