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Illustra and C<DBD::Illustra> support transactions.
The default transaction isolation level is Serializable.

Illustra supports all four standard isolation levels: Serializable,
Repeatable Read, Read Commited, and Read Uncommited.  The level be changed
per-transaction by executing a C<SET TRANSACTION ISOLATION LEVEL x>
statement where I<x> is the name of the isolation level required.

The default locking behavior is for readers to block writers.

Rows returned by a SELECT statement can be locked to prevent them from
being changed
by another transaction, by including "LOCK=EXCLUSIVE" or "LOCK=UPDATE" in the
optimizer hints for a given table:

  SELECT * FROM xyz USING(LOCK=UPDATE) WHERE xid = 'abc'

Exclusive locks provide less concurrency, but update locks must be
upgraded to exclusive when updates are required. This can cause
deadlock if another transaction has acquired a read lock in the
meantime.