(mysql.info) innodb-consistent-read

(mysql.info) innodb-transaction-isolation

(mysql.info) innodb-transaction-model

 
 14.2.10.4 Consistent Non-Locking Read
 .....................................
 
 A consistent read means that `InnoDB' uses multi-versioning to present
 to a query a snapshot of the database at a point in time. The query see
 the changes made by those transactions that committed before that point
 of time, and no changes made by later or uncommitted transactions. The
 exception to this rule is that the query sees the changes made by
 earlier statements within the same transaction.
 
 If you are running with the default `REPEATABLE READ' isolation level,
 all consistent reads within the same transaction read the snapshot
 established by the first such read in that transaction. You can get a
 fresher snapshot for your queries by committing the current transaction
 and after that issuing new queries.
 
 Consistent read is the default mode in which `InnoDB' processes `SELECT'
 statements in `READ COMMITTED' and `REPEATABLE READ' isolation levels. A
 consistent read does not set any locks on the tables it accesses, and
 therefore other users are free to modify those tables at the same time
 a consistent read is being performed on the table.
 
 Note that consistent read does not work over `DROP TABLE' and over
 `ALTER TABLE'.  Consistent read does not work over `DROP TABLE' because
 MySQL can't use a table that has been dropped and `InnoDB' destroys the
 table. Consistent read does not work over `ALTER TABLE' because it is
 executed inside of the transaction that creates a new table and inserts
 rows from the old table to the new table. When you reissue the
 consistent read, it will not see any rows in the new table, because
 they were inserted in a transaction that is not visible in the snapshot
 read by the consistent read.

Info Catalog

(mysql.info) innodb-transaction-isolation

(mysql.info) innodb-transaction-model

(mysql.info) innodb-locking-reads

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