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by Jiří {x2} Činčura

FbTransaction changes to support tables locking

8 Aug 2010 .NET, Firebird

Firebird has a feature allowing you to specify tables you want to lock (read or write and exclusive/protected/shared) when starting transaction. (Note that Firebird still uses MGA/MVCC. This is just a feature to support some scenarios.) We had constants in ADO.NET Provider for Firebird for some time, but using them resulted in wrong parameters being sent to the server and followed by exception. :)

Today I implemented support for this locking (tracker item, mailing list thread). That means sending proper sequences. The FbTransactionOptions class created earlier for timeout support was extended with new property LockTables. You can use to specify table name and lock specification. The lock specification there is in fact only subset of all options you can specify for transaction (same enumeration). You can put there whatever you want other options will be simply ignored.

Small example:

conn.BeginTransaction(new FbTransactionOptions()
		TransactionBehavior = FbTransactionBehavior.ReadCommitted,  // etc.
		LockTables = new Dictionary<string, FbTransactionBehavior>
			{ "TABLE_1", FbTransactionBehavior.LockWrite | FbTransactionBehavior.Shared },
			{ "TABLE_2", FbTransactionBehavior.LockWrite | FbTransactionBehavior.Exclusive }

Here I’m specifying that for TABLE_1 shared (huh :)) write lock will be placed and for TABLE_2 exclusive (that sounds better, isn’t it?) write lock will be placed. Similarly you can go with LockRead.

Available right now in weekly builds and SVN.