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90e035b6b0
Fixes #1890 Once rollback was implement we quickly saw that it lacked support for schema changes so we had to re-estructure things a bit. ## Example of failure: ```bash turso> begin; turso> create table t(x); turso> rollback; turso> pragma integrity_check; thread 'main' panicked at core/storage/sqlite3_ondisk.rs:386:36: called `Result::unwrap()` on an `Err` value: Corrupt("Invalid page type: 83") note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace ``` This happened because it thought table `t` existed because we didn't rollback that schema. ## Changes: * The most important change: now every connection has a private copy of schema. On write txn commit we update a global schema shared between connections in order for new connections to get updated version from there. In case of rollback, we simply change connection's schema to previous version. This change allowed us to remove locks for schema private copy and keeping schema changes locally in case of concurrency. Sqlite does things differently, they lazily parse schema in case of outdated schema, this many schema changes to trigger reading schema from db file which is slow. If we are able to keep local copy in memory, even when if we add multiprocessing, it will speed up schema reloading by a bunch. * `schema_cookie` is now update for every schema change * `Insn::ParseSchema` had a nasty bug where it would commit all the changes made in a query that changed a schema, we fixed that by setting `auto_commit` to `false` before parsing schema, and setting it back to previous value once schema is parsed. Closes #1928