23.  IBM solidDB

23.1. M-type tables vs. D-type tables
23.2. Concurrency control mechanism

Example 2.23.  Example properties for IBM solidDB

openjpa.ConnectionDriverName: solid.jdbc.SolidDriver
openjpa.ConnectionURL: jdbc:solid://localhost:2315/dba/dba

23.1.  M-type tables vs. D-type tables

IBM solidDB supports two types of tables: in-memory tables (M-tables) and on-disk tables (D-tables). Since cursor hold over commit can not apply to M-tables (which will cause SOLID Table Error 13187: The cursor cannot continue accessing M-tables after the transaction has committed or aborted. The statement must be re-executed), the default OpenJPA tables are D-tables. One can set the whole server to disk-based mode by adding [General] DefaultStoreIsMemory=no in solid.ini. The table types can also be determined by setting OpenJPA property "openjpa.jdbc.DBDictionary" with value "storeIsMemory=true" or "storeIsMemory=false" in the persistence.xml. The "STORE MEMORY" and "STORE DISK" will be appended to the create table DDL, respectively.

23.2.  Concurrency control mechanism

The default concurrency control mechanism depends on the table type: Disk-based tables (D-tables) are by default optimistic. Main-memory tables (M-tables) are always pessimistic. Since OpenJPA applications expects lock waits as usually is done with normal pessimistic databases, the server should be set to the pessimistic mode. The optimistic mode is about not waiting for the locks at all. That increases concurrency but requires more programming. The pessimistic mode with the READ COMMITTED isolation level (default) should get as much concurrency as one might need. The pessimistic locking mode can be set in solid.ini: [General] Pessimistic=yes One can override the locking mode on the per table base by setting OpenJPA property "openjpa.jdbc.DBDictionary" to value "lockingMode=PESSIMISTIC" in the persistence.xml. An extra SQL will be generated along with CREATE TABLE DDL: ALTER TABLE EX_POBJECT SET PESSIMISTIC. The possible values for lockingMode is OPTIMISTIC/PESSIMISTIC.