In addition to the existing `append_frame` which will write an individual frame
to the WAL, we add a method `append_frames_vectored` that takes N frames and the
db size which will need to be set for the last (commit) frame, and it
calculates the checksums and submits them as a single `pwritev` call,
reducing the number of syscalls needed for each write operation.
- Transaction which was started with max_frame = 0 and
max_frame_read_lock_index = 0 can write to the WAL and in this case it
needs to read data back from WAL and not the DB file.
- Without cache spilling its hard to reproduce this issue for the turso-
db now, but I found this issue with sync-engine which do weird stuff
with the WAL which "simulates" cache spilling behaviour to some extent.
Reviewed-by: Jussi Saurio <jussi.saurio@gmail.com>
Reviewed-by: Preston Thorpe <preston@turso.tech>
Closes#2735
- transaction which was started with max_frame = 0 and max_frame_read_lock_index = 0
can write to the WAL and in this case it needs to read data back from WAL
- without cache spilling its hard to reproduce this issue for the turso-db now,
but I stumbled into this issue with sync-engine which do weird stuff with the WAL
which "simulates" cache spilling behaviour to some extent
in #2521, I messed up and introduced improper calculation of the current
checkpoint's max safe frame (mostly due to incorrect comments that I had
left on the method).
The confusion partially stems from our lack of Busy handling at the
moment, but essentially when determining the max safe frame for all
readers, for passive mode we cannot simply `break` out of the loop when
we find a reader with a lower read mark than we have, because _another_
reader might have an even _lower_ read mark, and we could proceed with
the first mark < shared_max.
And for !passive modes, we still attempt to backfill with the same lower
frame, we just return `Busy` at the end, after backfilling what we can
(we just don't reset the log for restart/truncate).
Most of the changes in this PR is just the renaming the fields of
Checkpoint Result, because the names were confusing
Closes#2560
