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(mysql.info)InnoDB consistent read

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Consistent read
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A consistent read means that InnoDB uses its multiversioning to present
to a query a snapshot of the database at a point in time.  The query
will see the changes made by exactly 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 will see the
changes made by the transaction itself which issues the query.

When a transaction issues its first consistent read, InnoDB assigns the
snapshot, or the point of time, which all consistent reads in the same
transaction will use. In the snapshot are all transactions that
committed before assigning the snapshot. Thus the consistent reads
within the same transaction will also be consistent with respect to each
other. 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. 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.