As part of the drive to move over to flat_mutation_reader_v2, update
make_filtering_reader(). Since it doesn't examine range tombstones
(only the partition_start, to filter the key) the entire patch
is just glue code upgrading and downgrading users in the pipeline
(or removing a conversion, in one case).
Test: unit (dev)
Closes#9723
As part of changing the codebase to flat_mutation_reader_v2,
change chained_delegating_reader and its user virtual_table.
Since the reader does not process fragments (only forwarding
things around), only glue code is affected. It is also not
performance sensitive, so the extra conversions are unimportant.
Test: unit (dev)
Closes#9706
Symmetrically to virtual reader one, add the virtual writer
callback on a table that will be in charge of applying the
provided mutation.
If a virtual table doesn't override this apply method the
dedicated exception is thrown. Next patch will catch it and
propagate back to caller, so it's a new exception type, not
existing/std one.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Push down reversing to the mutation-sources proper, instead of doing it
on the querier level. This will allow us to test reverse reads on the
mutation source level.
The `max_size` parameter of `consume_page()` is now unused but is not
removed in this patch, it will be removed in a follow-up to reduce
churn.
The two might not be the same in case the schema was upgraded (unlikely
for virtual tables) or if we are reading in reverse. It is important to
use the passed-in query schema consistently during a read.
This patch flips two "switches":
1) It switches admission to be up-front.
2) It changes the admission algorithm.
(1) by now all permits are obtained up-front, so this patch just yanks
out the restricted reader from all reader stacks and simultaneously
switches all `obtain_permit_nowait()` calls to `obtain_permit()`. By
doing this admission is now waited on when creating the permit.
(2) we switch to an admission algorithm that adds a new aspect to the
existing resource availability: the number of used/blocked reads. Namely
it only admits new reads if in addition to the necessary amount of
resources being available, all currently used readers are blocked. In
other words we only admit new reads if all currently admitted reads
requires something other than CPU to progress. They are either waiting
on I/O, a remote shard, or attention from their consumers (not used
currently).
We flip these two switches at the same time because up-front admission
means cache reads now need to obtain a permit too. For cache reads the
optimal concurrency is 1. Anything above that just increases latency
(without increasing throughput). So we want to make sure that if a cache
reader hits it doesn't get any competition for CPU and it can run to
completion. We admit new reads only if the read misses and has to go to
disk.
Another change made to accommodate this switch is the replacement of the
replica side read execution stages which the reader concurrency
semaphore as an execution stage. This replacement is needed because with
the introduction of up-front admission, reads are not independent of
each other any-more. One read executed can influence whether later reads
executed will be admitted or not, and execution stages require
independent operations to work well. By moving the execution stage into
the semaphore, we have an execution stage which is in control of both
admission and running the operations in batches, avoiding the bad
interaction between the two.
This warning prevents using std::move() where it can hurt
- on an unnamed temporary or a named automatic variable being
returned from a function. In both cases the value could be
constructed directly in its final destination, but std::move()
prevents it.
Fix the handful of cases (all trivial), and enable the warning.
Closes#8992
This change adds a more specific implementation of the virtual table
called memtable_filling_virtual_table. It produces results by filling
a memtable on each read.
This change introduces the basic interface we expect each virtual
table to implement. More specific implementations will then expand
upon it if needed.
