Read uncommitted using Firebird FIBPlus components - delphi

Question

Using a TpFIBTransaction component, I'm trying to start a READ UNCOMMITTED transaction.
First of all, the TPBMode property has 3 possible values:
tpbDefault
tpbReadCommitted
tpbRepeatableRead
In TpFIBTransaction.StartTransaction I saw that setting tpbReadCommitted forces the following parameters:
write
isc_tpb_nowait
read_committed
rec_version
Using tpbRepeatableRead forces the following parameters instead:
write
isc_tpb_nowait
concurrency
So, it seems the only way to have "custom" transaction parameters is to set the tpbDefault value.
The values allowed for the TrParams property are the following (from fib.pas unit)
TPBConstantNames: array[1..isc_tpb_last_tpb_constant] of String = (
'consistency',
'concurrency',
'shared',
'protected',
'exclusive',
'wait',
'nowait',
'read',
'write',
'lock_read',
'lock_write',
'verb_time',
'commit_time',
'ignore_limbo',
'read_committed',
'autocommit',
'rec_version',
'no_rec_version',
'restart_requests',
'no_auto_undo',
'no_savepoint'
);
I've tried adding the 'read' value only, but it seems it's still unable to read uncommitted data, even if there's not 'read_committed' in TrParams property.
MyTransaction.TrParams.Clear();
MyTransaction.TrParams.Add('read');
Is there some missing value in TPBConstantNames (Something like 'read_uncommitted', if it exists...), or is there another way to setup a Firebird "read uncommitted" transaction?

Answer 1

It is not possible because Firebird does not support read uncomitted isolation level.
You can find the following information in the documentation documentation:
Note
The READ UNCOMMITTED isolation level is a synonym for READ
COMMITTED, and provided only for syntax compatibility. It provides the
exact same semantics as READ COMMITTED, and does not allow you to view
uncommitted changes of other transactions.
and:
The three isolation levels supported in Firebird are:
SNAPSHOT
SNAPSHOT TABLE STABILITY
READ COMMITTED with two specifications (NO RECORD_VERSION and
RECORD_VERSION)