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http://issues.apache.org/jira/browse/DERBY-1822?page=comments#action_12438181 ]
Mamta A. Satoor commented on DERBY-1822:
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Laura, I took a look at the page and the current structure of toursdb and have
come up with following example that can be used on the LOCK TABLE page. Hope
this helps
1)First of all, there is a typo in the first paragraph under Syntax. Rather
than 'Hotels', it should say 'Fights'. It should read as following
"Once a table is locked in either mode, a transaction does not acquire any
subsequent row-level locks on a table. For example, if a transaction locks the
entire Flights table in share mode in order to read data, a particular
statement might need to lock a particular row in exclusive mode in order to
update the row. However, the previous table-level lock on Flights forces the
exclusive lock to be table-level as well."
2)The updated example can look as follows
-- lock the entire table in share mode to avoid
-- a large number of row locks
LOCK TABLE Flights IN SHARE MODE;
SELECT *
FROM Flights
WHERE orig_airport > 'OOO';
-- lock the entire table in exclusive mode
-- for a transaction that will update many rows,
-- but where no single statement will update enough rows
-- to acquire an exclusive table lock on the table.
-- In a row-level locking system, that transaction would
-- require a large number of locks or might deadlock.
LOCK TABLE FlightAvailability IN EXCLUSIVE MODE;
UPDATE FlightAvailability
SET economy_seats_taken = (economy_seats_taken + 2)
WHERE flight_id = 'AA1265' AND flight_date = DATE('2004-03-31');
UPDATE FlightAvailability
SET economy_seats_taken = (economy_seats_taken + 2)
WHERE flight_id = 'AA1265' AND flight_date = DATE('2004-04-11');
UPDATE FlightAvailability
SET economy_seats_taken = (economy_seats_taken + 2)
WHERE flight_id = 'AA1265' AND flight_date = DATE('2004-04-12');
UPDATE FlightAvailability
SET economy_seats_taken = (economy_seats_taken + 2)
WHERE flight_id = 'AA1265' AND flight_date = DATE('2004-04-15');
-- if a transaction needs to look at a table before
-- updating it, acquire an exclusive lock before
-- selecting to avoid deadlocks
LOCK TABLE Maps IN EXCLUSIVE MODE;
SELECT MAX(map_id) + 1 from Maps;
-- INSERT INTO MAPS . . .
> LOCK TABLE example and description in reference manual should get replaced by
> a 'real' example
> ----------------------------------------------------------------------------------------------
>
> Key: DERBY-1822
> URL: http://issues.apache.org/jira/browse/DERBY-1822
> Project: Derby
> Issue Type: Bug
> Components: Documentation
> Affects Versions: 10.2.1.5, 10.3.0.0
> Reporter: Myrna van Lunteren
> Priority: Minor
> Fix For: 10.3.0.0
>
>
> The Example in the documentation for LOCK TABLE looks jumbled.
> It looks like part of it is based on a demo that was part of the pre-quel to
> Derby. The current toursdb demo is based on it, and thus includes reference
> to the table 'Flights', so it looks as if the queries *might* be possible,
> but the table listed (HotelAvailability) does not exist.
> Then there is mention of the table People, which doesn't exist either,
> A proper example needs to be put in place.
> Note that the description above the example mentions Hotels, this probably
> was supposed to be removed also.
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