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 Context VariablesSecurity 
NO WAIT Mode

In the NO WAIT mode, a transaction will immediately throw a database exception if a conflict occurs.

Note

LOCK TIMEOUT is a separate transaction option, but can only be used for WAIT transactions.Specifying LOCK TIMEOUT with a NO WAIT transaction will raise an error “invalid parameter in transaction parameter block -Option isc_tpb_lock_timeout is not valid if isc_tpb_nowait was used previously in TPB”
Isolation Level

Keeping the work of one database task separated from others is what isolation is about.Changes made by one statement become visible to all remaining statements executing within the same transaction, regardless of its isolation level.Changes that are in progress within other transactions remain invisible to the current transaction as long as they remain uncommitted.The isolation level and, sometimes, other attributes, determine how transactions will interact when another transaction wants to commit work.

The ISOLATION LEVEL attribute defines the isolation level for the transaction being started.It is the most significant transaction parameter for determining its behavior towards other concurrently running transactions.

The three isolation levels supported in Firebird are:

  • SNAPSHOT

  • SNAPSHOT TABLE STABILITY

  • READ COMMITTED with three specifications (READ CONSISTENCY, NO RECORD_VERSION and RECORD_VERSION)