Using cdsgroup_begin /* * Assume open dbenv (with DB_CDB_ALLDB) and two * open DBPs. Appropriate for multi-threaded applications that use multiple databases simultaneously. Allows open read cursor in a group during a write in the same group. Allows multiple write-cursors in a group.
Ĭdsgroup_begin Assigns a locker to a set of accesses called a group (like a transaction). cdsgroup_begin allocates a locker-id for a thread of control. Multiple threads of control (in the same process) accessing multiple databases can deadlock. In a multi-threaded process, locker IDs are allocated per cursor. Multi-threaded CDS Normally a locker-id is allocated per database. */ flags = DB_CREATE | DB_INIT_CDB ret = dbenv->open(dbenv, HOME, flags, 0) … error_handling … */ ret = dbenv->set_flags(dbenv, DB_CDB_ALLDB, 1) /* Create and open the environment. */ ret = db_env_create(&dbenv, 0) … error_handling … /* Turn on environment-wide locking. Ĭonfiguring DB_CDB_ALLDB /* Create handle. Appropriate for applications whose operations touch multiple databases. Simple, but … Low concurrency in presence of writes. No open read cursors in environment while writing. Only one write cursor in the entire environment. Performs locking on an environment-wide basis. If applications maintain open cursors on one database while operating on another database, concurrent operations can deadlock. Multiple Databases Normally CDS locks per-database. Ĭreating a write cursor (code) DBC *dbc = NULL ret = dbp->cursor(dbp, NULL, &dbc, DB_WRITECURSOR) if (ret != 0) … error_handling … Cursors that may write must be created with the DB_WRITECURSOR flag. Must avoid upgrading readlocks to writelocks. Applications can both read and write via cursors, so they need to be handled specially. Multiple readers in a single-database, OR Single writer in a database. */ flags = DB_CREATE | DB_INIT_CDB ret = dbenv->open(dbenv, HOME, flags, 0) … error_handling … ĬDS Locking CDS acquires locks at the API level.
*/ ret = db_env_create(&dbenv, 0) … error_handling … /* Create and open the environment. Setting up your Environment Environment required for CDS. ĬDS Programmatically Setting up your environment Write cursors Locking for complex applications Deadlock-free API-level locking What CDS does not do: Recovery Transactions Replication Part II: Concurrent Data Store Overview What is CDS? When is CDS appropriate? Case Studies Managing music Storing XML Ĭoncurrent Data Store Concurrency with reads and writes. Oracle Berkeley DB Concurrent Data Store A Use-Case Based Tutorial Oracle Berkeley DB - Concurrent Data Storage (CDS) Tutorial
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