On Aug 18, 2017, at 4:04 AM, sanhua.zh <sanhua...@foxmail.com> wrote:
> I am using SQLite in multi-thread mode, which means that different threads
> using different SQLite connection.
> And now I find an issue that the results of SQLite C interface returned is
> expired while the schema of database is changed.
>
>
> The following sample runs in different threads, but I force them to
> runsequentially.
>
>
> Thread 1:
> 1. Conn A: Open, PRAGMA journal_mode=WAL
> Thread 2:
> 2.ConnB: Open, PRAGMA journal_mode=WAL
> Thread 1:
> 3.ConnA: CREATE TABLE sample (i INTEGER);
> Thread 2:
> 4.ConnB: PRAGMA table_info('sample')
>
>
> Firstly, both thread 1 and 2 do initialization for their own conn, which is
> to read to schema into memory.
> Then, Conn A creates a table with Conn A.
> Finally, `PRAGMA table_info(sample)` is called in thread 2 with Conn B and it
> returns nothing.
> The same thing could happen if I change the step 4 to
> `sqlite3_table_column_metadata` or some other interfaces.
>
>
> I do know the reason should be the expired in-memory-schema. But I find no
> docs about which interface will or will not update the schema and what should
> I do while I call a non-update-schema interface ?
See the bottom of the sqlite3_prepare*() docs:
https://www.sqlite.org/c3ref/prepare.html
And the SQLITE_SCHEMA docs:
https://www.sqlite.org/rescode.html#schema
As the docs say, make sure you’re using sqlite3_prepare*_v2() or _v3(). If a
statement is prepared with these newer versions, it will handle most expiration
situations automatically by re-preparing the statement.
Generally speaking, if you do get an SQLITE_SCHEMA error, you need to rollback
the current transaction, re-prepare the statements, and try again.
-j
--
Jay A. Kreibich < J A Y @ K R E I B I.C H >
"Intelligence is like underwear: it is important that you have it, but showing
it to the wrong people has the tendency to make them feel uncomfortable." --
Angela Johnson
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