Paul wrote: >> pragma user_version; >> >> returns a single row with a single value which is the version, and the >> command, >> >> pragma user_version=n; >> >> lets you change it to n. Perhaps you can use this as a flag to tell yourself >> that you are working with an uninitialized database (value is 0), that >> another >> process is updating the database schema (change it to -1), or that it is at >> some internal revision number known to your program (it has a value > 0) such >> that you do not need to change the schema or initialize it. > > This is actually very helpful! > This soultion avoids unnecessary transaction after database open. > I can use *double checked locking* and start transaction only if necessary.
Please note that *all* accesses to the database file are done with transactions, including reading and writing the user_version value. This PRAGMA makes it slightly easier to check the database, but you cannot avoid transaction this way (or with any other way). (If the process correctly updates the database within a transaction, that value -1 would never be seen by another process.) Regards, Clemens _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
