When multiple tx writes happen concurrently in mvcc, max frame will be
updated. This new max_frame makes is the point of view of the other
transaction return busy because his current wal snapshot is outdated.
closes#3024
Also we snapshot the page when we determine that it's eligible, and pay a
memcpy instead of the read from disk, but this further prevents any in-memory
changes to the page/TOCTOU issues.
Our simulator is currently limited to concurrency of one. This
introduces a much less sophisticated DST with focus on finding
concurrency bugs.
Closes#2985
If both of the following are true:
1. All read locks are already held
2. The highest readmark of any read lock is less than the committed max frame
Then we must return Busy to the reader, because otherwise they would begin a
transaction with a stale local max frame, and thus not see some committed
changes.
Closes#1714
This PR enables the use of an index as the iteration cursor for a point
or range deletion operation. Main changes:
- Use `Delete` opcode for the index that is iterating the rows - avoids
unnecessary seeking on that index, since it's already positioned
correctly
- Fix delete balancing; details below:
### current state
- a deletion may cause a btree rebalancing operation
- to get the cursor back to the right place after a rebalancing, we must
remember what the deleted key was and seek to it
- right now we are using `SeekOp::LT` to move to one slot BEFORE the
deleted key, so that if we delete rows in a loop, the following `Next()`
call will put us back into the right place
### problem
- When we delete multiple rows, we always iterate forwards. Using
`SeekOp::LT` implies backwards iteration, but it works OK for table
btrees since the cursor never remains on an internal node, because table
internal cells do not have payloads. However: this behavior is
problematic for indexes because we can effectively end up skipping
visiting a page entirely. Honestly: despite spending some debugging the
_old_ code, I still don't remember what exactly causes this to happen.
:) It's one of the `iter_dir` specific behaviors in `indexbtree_move_to`
or `get_prev_record()`, but I'm too tired to spend more time figuring it
out. I had the reason in my head before going on vacation, but it was
evicted from the cache it seems...
### solution
use `SeekOp::GE { eq_only: true }` instead and make the next call to
`Next()` a no-op instead. This has the same effect as SeekOp::LT +
next(), but without introducing bugs due to `LT` being implied backwards
iteration.
Reviewed-by: Nikita Sivukhin (@sivukhin)
Closes#2981
The `run_once()` name is just a historical accident. Furthermore, it now
started to appear elsewhere as well, so let's just call it IO::step() as we
should have from the beginning.
Because `io_uring` may have many other I/O submission events queued
(that are relevant to the operation) when we experience an error,
marking our `Completion` objects as aborted is not sufficient, the
kernel will still execute queued I/O, which can mutate WAL or DB state
after we’ve declared failure and keep references (iovec arrays, buffers)
alive and stall reuse. We need to stop those in-flight SQEs at the
kernel and then drain the ring to a known-empty state before reusing any
resources.
The following methods were added to the `IO` trait:
`cancel`: which takes a slice of `Completion` objects and has a default
implementation that simply marks them as `aborted`.
`drain`: which has a default noop implementation, but the `io_uring`
backend implements this method to drain the ring.
CC @sivukhin
Reviewed-by: Pere Diaz Bou <pere-altea@homail.com>
Closes#2787
Previously we were iterating over every entry in the page cache,
clearing the dirty flag from each page.
Reviewed-by: Pere Diaz Bou <pere-altea@homail.com>
Reviewed-by: Nikita Sivukhin (@sivukhin)
Closes#2988
