This commit ensures that the metadata in the database header and the pointer map pages allocated are correctly persisted to the page cache. This was not being done earlier.
This commit introduces AUTOVACUUM to Limbo. It introduces the concept of ptrmap pages and also adds some additional instructions that are required to make AUTOVACUUM PRAGMA work
- 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
One problem we have with PageRef, is that this Page reference can be
unloaded, this means if we read the page again instead of loading the
page onto the same reference, we will have split brain of references.
To solve this we wrap PageRef in `BTreePage` so that if a page is seen
as unloaded, we will replace BTreePage::page with the newest version of
the page.
After inserting a page into the wal, we dispose of the modified page.
This is unnecessary as we can simply move new page to the newest
snapshot where this page can be read.
Dirty pages can be deleted in `cacheflush`. Furthermore, there could be
multiple live references in the stack of a cursor so let's allow them to
exist while deleting.
insert() fails if key exists (there shouldn't be two) and panics if
it's different pages, and also fails if it can't make room for the page.
Replaced the limited pop_if_not_dirty() function with make_room_for().
It tries to evict many pages as requested spare capacity. It should come
handy later by resize() and Pager. make_room_for() tries to make room or
fails if it can't evict enough entries.
For make_room_for() I also tried with an all-or-nothing approach, so if
say a query requests a lot more than possible to make room for, it
doesn't evict a bunch of pages from the cache that might be useful. But
implementing this approach got very complicated since it needs to keep
exclusive PageRefs and collecting this caused segfaults. Might be worth
trying again in the future. But beware the rabbit hole.
Updated page cache test logic for new insert rules.
Updated Pager.allocate_page() to handle failure logic but needs further
work. This is to show new cache insert handling. There are many places
to update.
Left comments on callers of pager and page cache needing to update
error handling, for now.
"Open a new cursor P1 to a transient table. The cursor is always opened read/write even if the main database is read-only. The ephemeral table is deleted automatically when the cursor is closed.
If the cursor P1 is already opened on an ephemeral table, the table is cleared (all content is erased)."
There is still some work to do, but this is a basic setup
Passing 1s and 0s with comments is not rustacean, and since we already follow the pattern of struct flags in other sections of the codebase it's better use it here too.
We assumed page was loaded because before inserting we would move there.
`NewRowId` unfortunately moves cursor to the rightmost page causing
eviction of root page -- this arose the issue with `insert_into_page`
not loading the page we were supposed to have loaded so I added
`return_if_locked_maybe_load` which is a utility macro to check if the
page is locked and if not, load it if needed.
Closes#1138
We assumed page was loaded because before inserting we would move there. `NewRowId` unfortunately moves cursor to the rightmost page causing eviction of root page -- this arose the issue with `insert_into_page` not loading the page we were supposed to have loaded so I added `return_if_locked_maybe_load` which is a utility macro to check if the page is locked and if not, load it if needed.
We need to ensure an operation doesn't transform the cells inside a page
to an invalid state. In debug mode we can enable a
`debug_validate_cells` with `#[cfg(debug_assertions)]` so that it is
skipped on release mode.
Modify pager logs
- Use `CheckpointResult::default()` instead of `CheckpointResult::new()`
- Correct WAL frame header salt and checksum handling
- Ensure frame ID is 1-based and adjust frame offset calculation
- Add `Default` implementation for `CheckpointResult`
- Use random values for WAL header salts
