Hi Enno,
Forgive me for a possibly stupid question, but why this feature is so badly
needed?
What's wrong with populating database to a desired state, shutting down,
copying the file, and starting H2 with a file copy.
Why do you need this functionality for in-memory (non-persistent) database?
If performance is the reason, you can use RAM-based file system instead.
I am struggling to understand what is going to happen with all other
concurrent connections and their transactions at the moment when RESTORE TO
POINT is executed.
I also agree with Evgenij, that implementation based on MVStore will
prevent a lot of intermediate versions from being dropped and heedlessly
bloat database file.
Regards,
Andrei
On Friday, November 8, 2024 at 8:48:33 PM UTC-5 Evgenij Ryazanov wrote:
> Don't use labdas in unit tests at all unless it is strongly necessary.
> Write a single method for each test case with plain code, if in needs to be
> tested with different setup, pass parameters to this method and invoke it
> multiple times. Take a look on existing unit tests for examples.
>
> I changed execute(boolean autoCommit, SQLUnit... units) to re-open
> connection and tests started to fail, but maybe I did something wrong.
> Anyway, such method shouldn't exist, because it's hard to add some
> additional operation (such as mentioned reconnection) to existing tests ad
> debugging is also complicated.
>
> This code throws OOME unless restore point creation is commented out:
>
> Connection conn = DriverManager.getConnection("jdbc:h2:mem:1");
>
> Statement stat = conn.createStatement();
>
> stat.execute("CREATE TABLE TEST(ID BIGINT GENERATED ALWAYS AS IDENTITY
> PRIMARY KEY, V BINARY VARYING)");
>
> stat.execute("CREATE RESTORE POINT P");
>
> PreparedStatement prepInsert = conn.prepareStatement("INSERT INTO TEST(V)
> VALUES ?");
>
> PreparedStatement prepDelete = conn.prepareStatement("DELETE FROM TEST");
>
> for (;;) {
>
> prepInsert.setBytes(1, new byte[1_000_000]);
>
> prepInsert.executeUpdate();
>
> prepDelete.executeUpdate();
>
> }
>
> This code throws General Error:
>
> DeleteDbFiles.execute(".", "rptest1", false);
>
> Connection conn = DriverManager.getConnection(
> "jdbc:h2:./rptest1;DEFRAG_ALWAYS=TRUE");
>
> Statement stat = conn.createStatement();
>
> stat.execute("CREATE TABLE TEST(ID BIGINT GENERATED ALWAYS AS IDENTITY
> PRIMARY KEY, V INT)");
>
> PreparedStatement prepInsert = conn.prepareStatement("INSERT INTO TEST(V)
> VALUES ?");
>
> prepInsert.setInt(1, 1);
>
> prepInsert.executeUpdate();
>
> stat.execute("CREATE RESTORE POINT P");
>
> for (int i = 2; i <= 100; i++) {
>
> prepInsert.setInt(1, i);
>
> prepInsert.executeUpdate();
>
> }
>
> conn.close();
>
> conn = DriverManager.getConnection("jdbc:h2:./rptest1");
>
> stat = conn.createStatement();
>
> stat.execute("RESTORE TO POINT P");
>
> ResultSet rs = stat.executeQuery("SELECT COUNT(*) FROM TEST");
>
> rs.next();
>
> System.out.println(rs.getLong(1));
>
> It is possible to write a more complex code where RESTORE TO POINT will
> silently restore to the wrong version. I think you can document that
> database compaction may erase restore points, but in this case you need to
> remove their metadata as well to prevent possibility to execute these
> commands with outdated versions.
>
> Because SCRIPT command can't export these restore points, it must be
> documented.
>
> You also need to document this functionality as experimental only.
>
> I think content of INFORMATION_SCHEMA.RESTORE_POINTS shouldn't be visible
> for regular users. Don't use MVCC in its documentation, this term only
> confuses people.
>
> What is a purpose of OLDEST_DATABASE_VERSION_TO_KEEP and why this field
> isn't changed in newer restore points if older restore points were already
> dropped?
>
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