What is the level of consistency (or rather inconsistency) for read_uncommitted?
If you start with: INSERT INTO Woz(Foo, Bar) Values(1,1) And a (normal) writer thread updates the 2 columns: UPDATE Woz SET Foo=2, Bar=2 Can a read_uncommitted thread read the value from the row as: Foo=1, Bar=2 ? And if so, what about something like: UPDATE Woz SET Foo=2, Bar=x'12345789' Can a read_uncommitted thread read: Foo=x'12340000' i.e. A partially updated column? I would assume that for a transactional update across 2 rows all bets will be off. What if a row was deleted, can a read_uncommitted read cause a crash? - Deon -----Original Message----- From: sqlite-users [mailto:sqlite-users-boun...@mailinglists.sqlite.org] On Behalf Of Simon Slavin Sent: Friday, January 19, 2018 8:36 AM To: SQLite mailing list <sqlite-users@mailinglists.sqlite.org> Subject: Re: [sqlite] WAL and pragma uncommitted On 19 Jan 2018, at 4:26pm, Hannah Massey <hannah.bea...@gmail.com> wrote: > Will #pragma uncommitted work in WAL mode and will it have the effect > I'm looking for (where the read will be faster because it can ignore > the recently written information in the WAL File) and simply use the > database file only? The command you’re talking about is PRAGMA read_uncommitted = boolean You may find you don’t need it. Switch to WAL mode and try it without that PRAGMA. It works more or less the way you described: one connection can write while other read, and nothing will block anything else. Pay a lot of attention to how many connections you’re using. You might want one connection for the writing, and another for all the reading threads. Or you might want separate connections for the reading threads too. Testing various approaches will let you find the solution which best suits your programming and timing requirements. Simon. _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org https://nam01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fmailinglists.sqlite.org%2Fcgi-bin%2Fmailman%2Flistinfo%2Fsqlite-users&data=02%7C01%7C%7C7304a7658ee04115fe6508d55f5abc8e%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636519765662668955&sdata=o6sR0H3YrZMdFUm9OwJ3CjyYi3J9s0MapK2%2BBeoiBuY%3D&reserved=0 _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
