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https://issues.apache.org/jira/browse/DERBY-3185?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12541008
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Bernt M. Johnsen commented on DERBY-3185:
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The following statement in
http://db.apache.org/derby/docs/dev/ref/rrefsqlj41180.html is also misleading:
"The JDBC java.sql.Connection.setTransactionIsolation method behaves almost
identically to this command, with one exception: if you are using the embedded
driver, and if the call to java.sql.Connection.setTransactionIsolation does not
actually change the isolation level (that is, if it sets the isolation level to
its current value), the current transaction is not committed."
There is *TWO* exceptions: The one mentioned, AND the fact that "REPEATABLE
READ" in SQL is NOT the same isolation level as
Connection.TRANSACTION_REPEATABLE_READ.
Most users will assume they are the same and never bother to read the docs.
When they encounter problems the user will still not read the docs because it's
so obvious that the two should be interpreted as the same isolation level. When
posting on derby-user/derby-dev about this "bug", the response would be a
(presumably) polite pointer to the docs and the user (which doesn't know the
history and most likely does't care about DB2 compatability) will wonder what
the developers where thinking when they implemented it like this.
I think we should 1) interpret SQL REPEATABLE READ according to the SQL
standard, and 2) implement a SQL compatible SET TRANSACTION ISOLATION statement.
> SET (TRANSACTION) ISOLATION (LEVEL) is not SQL compliant
> --------------------------------------------------------
>
> Key: DERBY-3185
> URL: https://issues.apache.org/jira/browse/DERBY-3185
> Project: Derby
> Issue Type: Bug
> Components: JDBC, SQL
> Affects Versions: 10.3.1.4
> Reporter: Dyre Tjeldvoll
>
> The SQL standard (2003) requires the keyword 'TRANSACTION' and allows the
> keyword 'LEVEL' in
> SET TRANSACTION ISOLATION LEVEL <level> Derby permits neither and issues a
> syntax error (but permits the optional word 'CURRENT').
> There is also an inconsistency between JDBC and SQL when specifying
> 'repeatable read' isolation level.
> Specifying repeatable read from JDBC works as expected:
> conn.setTransactionIsolation(Connection.TRANSACTION_REPEATABLE_READ);
> assert(conn.getTransactionIsolation() ==
> Connection.TRANSACTION_REPEATABLE_READ) // OK
> Doing it in SQL yields RR or
> SET ISOLATION REPEATABLE READ;
> VALUES CURRENT ISOLATION; -> RR
> assert(conn.getTransactionIsolation() ==
> Connection.TRANSACTION_REPEATABLE_READ) // FAILS, RR is translated into
> Connection.TRANSACTION_SERIALIZABLE
> Using RS in SQL works as expected
> SET ISOLATION RS;
> VALUES CURRENT ISOLATION; -> RS
> assert(conn.getTransactionIsolation() ==
> Connection.TRANSACTION_REPEATABLE_READ) // OK
> I guess there could be backward compatibility issues that makes it difficult
> to change this,
> but the current behavior is really confusing and should at least be better
> documented. An alternative is to add a new
> SQL compliant SET TRANSACTION which uses the standard isolation level
> specifiers, and keep SET (CURRENT) ISOLATION as it is today for backward
> compatibility.
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