Thanks for everyone. You are right. According to you help, I understand the problem. Just open or attach database , open operation is faster than attach database. if add a query statement after open or attach database. The time which they cost almost the same.
Best regards. what Dominique said is right. As following: Anyway, I remember observing that: - sqlite3_open_v2(...) is lazy. In other words, it does not parse the schema of the DB until the first query is performed after opening the database. - ATTACH is not lazy. The schema is parsed as soon as you attach a database. That could explain the difference in speed. Would there be a way to make ATTACH lazy by the way? Regards Dominique At 2015-12-16 18:27:34, "Dan Kennedy" <danielk1977 at gmail.com> wrote: >On 12/16/2015 12:51 PM, ??? wrote: >> After testing the Sqlite3_open and ATTACH DATABASE, >> I found that the attach database is slower than sqlite3_open. >> there is attachment after the mail which includ the speed >> information ( millisecond ). > >Hi, > >This mailing list strips attachments, so you'll need to include the >information inline. > >One possible explanation: When you run an ATTACH statement, SQLite opens >the new database file and reads the schema from the sqlite_master table. >Whereas sqlite3_open() just opens the db file (reading the schema is >deferred until it is first required in this case). > >So an apples/apples comparison might be to open/ATTACH the database and >then run a simple query that forces SQLite to read the database schema >if it has not already - say "SELECT * FROM sqlite_master". > >Dan. > > >_______________________________________________ >sqlite-users mailing list >sqlite-users at mailinglists.sqlite.org >http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
