MySql support for pessimistic transaction

Question

Hello,
I am using kodo 2.5.3 against mySql 4.0.13.
I am experiencing strange behaviors using pessimistic transactions.
Indeed, the Select for update generated by kodo does not seems to lock the
row concerned.
Then, I found in the Kodo documentation that the MySQLDictionary
understands the following property :
SupportsSelectForUpdate (Default: true)
Description: If true, then assume that this MySQL install is capable of
locking data on select, using SELECT ... FOR UPDATE syntax. Otherwise,
assume that this MySQL install cannot lock data. Currently, Kodo JDO
silently ignores requests to obtain pessimistic locks in this situation.
In the future, Kodo JDO will throw an exception if configured with data
store exceptions while this is false.
So, does it means that something special has to be done on the mySql side
to "activate" row locking when using select for update ?
Thank You,
Christophe
PS : In my understanding of rows locking using select for update, rows are
locked also for reading, I guess this is not a bad assumption.

Answer 1

Thank You Marc,
Pessimistic locking works fine when setting TableType=InnoDB.
Christophe
Marc Prud'hommeaux wrote:
Christophe-
In order to use pessimistic locking, you need to use a table type that
supports locking (the defauly "MyISM" tables do not). The "InnoDB" table
types do support locking (as well as other nice features like foreign
keys).
If you have Kodo generating your tables, you can specify that Kodo
should create tables of type InnoDB with the "TableType" dictionary
property (see docs). Otherwise, you would need to migrate the tables on
the database manually.
In article <blls3c$5k7$[email protected]>, Christophe Darville wrote:
Hello,
I am using kodo 2.5.3 against mySql 4.0.13.
I am experiencing strange behaviors using pessimistic transactions.
Indeed, the Select for update generated by kodo does not seems to lock the
row concerned.
Then, I found in the Kodo documentation that the MySQLDictionary
understands the following property :
SupportsSelectForUpdate (Default: true)
Description: If true, then assume that this MySQL install is capable of
locking data on select, using SELECT ... FOR UPDATE syntax. Otherwise,
assume that this MySQL install cannot lock data. Currently, Kodo JDO
silently ignores requests to obtain pessimistic locks in this situation.
In the future, Kodo JDO will throw an exception if configured with data
store exceptions while this is false.
So, does it means that something special has to be done on the mySql side
to "activate" row locking when using select for update ?
Thank You,
Christophe
PS : In my understanding of rows locking using select for update, rows are
locked also for reading, I guess this is not a bad assumption.
Marc Prud'hommeaux [email protected]
SolarMetric Inc. http://www.solarmetric.com