SQLite behavior is: if another connection has modified the DB when a
read tx starts, it must clear its page cache due to the potentiality
of there being stale versions of pages in it.
In the future, we may want to do either:
1. a more granular invalidation logic for per-conn cache, or
2. a shared versioned page cache
But right now we must follow SQLite to make our current behavior not
corrupt data
`BTreeTable::to_sql` makes us incompatible with SQLite by losing e.g. the original whitespace provided during the CREATE TABLE command.
For now let's fix our tests by regex-replacing every CREATE TABLE in
the entire repo to have exactly 1 space after the table name in the
CREATE TABLE statement.
Makes it easier to test the feature:
```
$ cargo run -- --experimental-indexes
Limbo v0.0.22
Enter ".help" for usage hints.
Connected to a transient in-memory database.
Use ".open FILENAME" to reopen on a persistent database
limbo> CREATE TABLE t(x);
limbo> CREATE INDEX t_idx ON t(x);
limbo> DROP INDEX t_idx;
```
We were incorrectly setting `moved_before` as `false` after checking
for unique constraint violation, but the reality is that after the
uniqueness check, we are already correctly positioned -- if no match
was found, the cursor is positioned at either:
a) no row, or
b) at the first entry that is greater than the key we are inserting.
This means we don't have to move anymore and can just insert.
- Instead of using a confusing CheckpointStatus for many different things,
introduce the following statuses:
* PagerCacheflushStatus - cacheflush can result in either:
- the WAL being written to disk and fsynced
- but also a checkpoint to the main BD file, and fsyncing the main DB file
Reflect this in the type.
* WalFsyncStatus - previously CheckpointStatus was also used for this, even
though fsyncing the WAL doesn't checkpoint.
* CheckpointStatus/CheckpointResult is now used only for actual checkpointing.
- Rename HaltState to CommitState (program.halt_state -> program.commit_state)
- Make WAL a non-optional property in Pager
* This gets rid of a lot of if let Some(...) boilerplate
* For ephemeral indexes, provide a DummyWAL implementation that does nothing.
- Rename program.halt() to program.commit_txn()
- Add some documentation comments to structs and functions
### What?
adding checkpoint result returning number of pages in wal and num pages
checkpointed.
Part of #696
### Context
SQLite returns in checkpoint result of calling `pragma wal_checkpoint;`
`0|3|3` while limbo returns `0|0|0`.
https://sqlite.org/pragma.html#pragma_wal_checkpoint
- 1st col: 1 (checkpoint SQLITE_BUSY) or 0 (not busy).
- 2nd col: # modified pages written to wal file
- 3rd col: # pages moved to db after checkpoint
This PR aims to add 2nd and 3rd column to the checkpoint result.
SQLite
```
sqlite3 test.db
sqlite> pragma journal_mode=wal;
wal
sqlite> pragma journal_mode;
wal
sqlite> create table t1 (id text);
sqlite> insert into t1(id) values (1),(2);
sqlite> select * from t1;
1
2
sqlite> pragma wal_checkpoint;
0|3|3
```
Limbo
```
./target/debug/limbo test.db
Limbo v0.0.13
Enter ".help" for usage hints.
limbo> pragma journal_mode;
wal
limbo> create table t1(id text);
limbo> insert into t1(id) values (1),(2);
limbo> select * from t1;
1
2
# current the 2nd and 3rd columns are hard coded in limbo to 0
limbo> pragma wal_checkpoint;
0|0|0
```
Closes#827
