### The problem:
I often need to copy the output of an `Explain` statement to my
clipboard. Currently this is not possible because it currently will only
write to stdout.
All other limbo output, I am able to run `.output file` in the CLI, then
enter my query and in another tmux pane I simply `cat file | xclip -in
-selection clipboard`.
### The solution:
Expose a `statement.explain()` method that returns the query explanation
as a string. If the user uses something like `execute` instead of
prepare, it will default to `stdout` as expected, but this allows the
user to access the query plan on the prepared statement and do with it
what they please.
Closes#1166
This PR adds support for `DROP TABLE` and addresses issue
https://github.com/tursodatabase/limbo/issues/894
It depends on https://github.com/tursodatabase/limbo/pull/785 being
merged in because it requires the implementation of `free_page`.
EDIT: The PR above has been merged.
It adds the following:
* an implementation for the `DropTable` AST instruction via a method
called `translate_drop_table`
* a couple of new instructions - `Destroy` and `DropTable`. The former
is to modify physical b-tree pages and the latter is to modify in-memory
structures like the schema hash table.
* `btree_destroy` on `BTreeCursor` to walk the tree of pages for this
table and place it in free list.
* state machine traversal for both `btree_destroy` and
`clear_overflow_pages` to ensure performant, correct code.
* unit & tcl tests
* modifies the `Null` instruction to follow SQLite semantics and accept
a second register. It will set all registers in this range to null. This
is required for `DROP TABLE`.
The screenshots below have a comparison of the bytecodes generated via
SQLite & Limbo.
Limbo has the same instruction set except for the subroutines which
involve opening an ephemeral table, copying over the triggers from the
`sqlite_schema` table and then re-inserting them back into the
`sqlite_schema` table.
This is because `OpenEphemeral` is still a WIP and is being tracked at
https://github.com/tursodatabase/limbo/pull/768
Reviewed-by: Pere Diaz Bou <pere-altea@homail.com>
Closes#897
modified the Null instruction to more closely match SQLite semantics. Allows passing in a second register and all registers from r1..r2 area set to null
- right-nested expression can generate multiple labels which needs to be
resolved to next generated instruction
- for example, COALESCE(0, COALESCE(0, 1))
Use knowledge of query plan to inform how much memory to initially
allocate for `ProgramBuilder` vectors
Some of them are exact, some are semi-random estimates
```sql
Prepare `SELECT 1`/Limbo/SELECT 1
time: [756.93 ns 758.11 ns 759.59 ns]
change: [-4.5974% -4.3153% -4.0393%] (p = 0.00 < 0.05)
Performance has improved.
Found 7 outliers among 100 measurements (7.00%)
2 (2.00%) low severe
1 (1.00%) low mild
3 (3.00%) high mild
1 (1.00%) high severe
Prepare `SELECT * FROM users LIMIT 1`/Limbo/SELECT * FROM users LIMIT 1
time: [1.4739 µs 1.4769 µs 1.4800 µs]
change: [-7.9364% -7.7171% -7.4979%] (p = 0.00 < 0.05)
Performance has improved.
Found 1 outliers among 100 measurements (1.00%)
1 (1.00%) high mild
Prepare `SELECT first_name, count(1) FROM users GROUP BY first_name HAVING count(1) > 1 ORDER BY cou...`
time: [3.7440 µs 3.7520 µs 3.7596 µs]
change: [-5.4627% -5.1578% -4.8445%] (p = 0.00 < 0.05)
Performance has improved.
Found 1 outliers among 100 measurements (1.00%)
1 (1.00%) high severe
```
Closes#899
The main difference between = and != is how null values are handled.
SQLite passes a flag "NULLEQ" to Eq and Ne to disambiguate that.
In the presence of that flag, NULL = NULL.
Some prep work is done to make sure we can pass a flag instead of a
boolean to Eq and Ne. I looked into the bitflags crate but got a bit
scared with the list of dependencies.
Warning:
The following query produces a different result for Limbo:
```
select * from demo where value is null or id == 2;
```
I strongly suspect the issue is with the OR implementation, though. The
bytecode generated is quite different.
Reviewed-by: Jussi Saurio <jussi.saurio@gmail.com>
Closes#847
Instead of always having the caller specify all instructions, this
work introduces convenience functions into the program builder,
making the code a lot cleaner.
TLDR: no need to call either of:
program.emit_insn_with_label_dependency() -> just call program.emit_insn()
program.defer_label_resolution() -> just call program.resolve_label()
Changes:
- make BranchOffset an explicit enum (Label, Offset, Placeholder)
- remove program.emit_insn_with_label_dependency() - label dependency is automatically detected
- for label to offset mapping, use a hashmap from label(negative i32) to offset (positive u32)
- resolve all labels in program.build()
- remove program.defer_label_resolution() - all labels are resolved in build()
