Commit Graph

717 Commits

Author SHA1 Message Date
Raphael S. Carvalho
da04fea71e compaction: Fix key estimation per sstable to produce efficient filters
The estimation assumes that size of other components are irrelevant,
when estimating the number of partitions for each output sstable.
The sstables are split according to the data file size, therefore
size of other files are irrelevant for the estimation.

With certain data models, like single-row partitions containing small
values, the index could be even larger than data.
For example, assume index is as large as data, then the estimation
would say that 2x more sstables will be generated, and as a result,
each sstable are underestimated to have 2x less keys.

Fix it by only accounting size of data file.

Fixes #15726.

Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>

Closes scylladb/scylladb#15727
2023-10-17 11:21:11 +03:00
Aleksandra Martyniuk
f42be12f43 repair: release resources of shard_repair_task_impl
Before integration with task manager the state of one shard repair
was kept in repair_info. repair_info object was destroyed immediately
after shard repair was finished.

In an integration process repair_info's fields were moved to
shard_repair_task_impl as the two served the similar purposes.
Though, shard_repair_task_impl isn't immediately destoyed, but is
kept in task manager for task_ttl seconds after it's complete.
Thus, some of repair_info's fields have their lifetime prolonged,
which makes the repair state change delayed.

Release shard_repair_task_impl resources immediately after shard
repair is finished.

Fixes: #15505.

Closes scylladb/scylladb#15506
2023-09-26 17:09:47 +03:00
Botond Dénes
d5f095d5a4 Merge 'Make interaction of compaction strategy with sstable runs more robust and efficient' from Raphael "Raph" Carvalho
SSTable runs work hard to keep the disjointness invariant, therefore they're
expensive to build from scratch.
For every insertion, it keeps the elements sorted by their first key in
order to reject insertion of element that would introduce overlapping.

Additionally, a sstable run can grow to dozens of elements (or hundreds)
therefore, we can also make interaction with compaction strategies more
efficient by not copying them when building a list of candidates in compaction
manager. And less fragile by filtering out any sstable runs that are not
completely eligible for compaction.

Previously, ICS had to give up on using runs managed by sstable set due to
fragility of the interface (meaning runs are being built from scratch
on every call to the strategy, which is very inefficient, but that had to
be done for correctness), but now we can restore that.

Closes scylladb/scylladb#15440

* github.com:scylladb/scylladb:
  compaction: Switch to strategy_control::candidates() for regular compaction
  tests: Prepare sstable_compaction_test for change in compaction_strategy interface
  compaction: Allow strategy to retrieve candidates either as sstables or runs
  compaction: Make get_candidates() work with frozen_sstable_run too
  sstables: add sstable_run::run_identifier()
  sstables: tag sstable_run::insert() with nodiscard
  sstables: Make all_sstable_runs() more efficient by exposing frozen shared runs
  sstables: Simplify sstable_set interface to retrieve runs
2023-09-26 14:56:05 +03:00
Aleksandra Martyniuk
d799adc536 tasks: change task_manager::task::impl::is_internal()
Most of the time only the roots of tasks tree should be non internal.

Change default implementation of is_internal and delete overrides
consistent with it.

Closes scylladb/scylladb#15353
2023-09-26 14:49:49 +03:00
Raphael S. Carvalho
8997fe0625 compaction: Switch to strategy_control::candidates() for regular compaction
Now everything is prepared for the switch, let's do it.

Now let's wait for ICS to enjoy the set of changes.

Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
2023-09-25 17:18:21 -03:00
Raphael S. Carvalho
02f1f24f27 compaction: Allow strategy to retrieve candidates either as sstables or runs
That's needed for upcoming changes that will allow ICS to efficiently
retrieve sstable runs.

Next patch will remove candidates from compaction_strategy's interface
to retrieve candidates using this one instead.

Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
2023-09-25 17:18:21 -03:00
Raphael S. Carvalho
ff8510445d compaction: Make get_candidates() work with frozen_sstable_run too
This is done in preparation for ICS to retrieve candidates as
sstable runs.

Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
2023-09-25 17:18:21 -03:00
Avi Kivity
61440d20c3 Merge 'Enable incremental compaction on off-strategy' from Raphael "Raph" Carvalho
Off-strategy suffers with a 100% space overhead, as it adopted
a sort of all or nothing approach. Meaning all input sstables,
living in maintenance set, are kept alive until they're all
reshaped according to the strategy criteria.

Input sstables in off-strategy are very likely to be mostly disjoint,
so it can greatly benefit from incremental compaction.

The incremental compaction approach is not only good for
decreasing disk usage, but also memory usage (as metadata of
input and output live in memory), and file desc count, which
takes memory away from OS.

Turns out that this approach also greatly simplifies the
off-strategy impl in compaction manager, as it no longer have
to maintain new unused sstables and mark them for
deletion on failure, and also unlink intermediary sstables
used between reshape rounds.

Fixes https://github.com/scylladb/scylladb/issues/14992.

Closes scylladb/scylladb#15400

* github.com:scylladb/scylladb:
  test: Verify that off-strategy can do incremental compaction
  compaction: Clear pending_replacement list when tombstone GC is disabled
  compaction: Enable incremental compaction on off-strategy
  compaction: Extend reshape type to allow for incremental compaction
  compaction: Move reshape_compaction in the source
  compaction: Enable incremental compaction only if replacer callback is engaged
2023-09-21 20:12:19 +03:00
Raphael S. Carvalho
9d92374b20 compaction: Clear pending_replacement list when tombstone GC is disabled
pending_replacement list is used by incremental compaction to
communicate to other ongoing compactions about exhausted sstables
that must be replaced in the sstable set they keep for tombstone
GC purposes.

Reshape doesn't enable tombstone GC, so that list will not
be cleared, which prevents incremental compaction from releasing
sstables referenced by that list. It's not a problem until now
where we want reshape to do incremental compaction.

Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
2023-09-21 11:15:46 -03:00
Raphael S. Carvalho
42050f13a0 compaction: Enable incremental compaction on off-strategy
Off-strategy suffers with a 100% space overhead, as it adopted
a sort of all or nothing approach. Meaning all input sstables,
living in maintenance set, are kept alive until they're all
reshaped according to the strategy criteria.

Input sstables in off-strategy are very likely to mostly disjoint,
so it can greatly benefit from incremental compaction.

The incremental compaction approach is not only good for
decreasing disk usage, but also memory usage (as metadata of
input and output live in memory), and file desc count, which
takes memory away from OS.

Turns out that this approach also greatly simplifies the
off-strategy impl in compaction manager, as it no longer have
to maintain new unused sstables and mark them for
deletion on failure, and also unlink intermediary sstables
used between reshape rounds.

Fixes #14992.

Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
2023-09-21 11:15:46 -03:00
Raphael S. Carvalho
db9ce9f35a compaction: Extend reshape type to allow for incremental compaction
That's done by inheriting regular_compaction, which implement
incremental compaction. But reshape still implements its own
methods for creating writer and reader. One reason is that
reshape is not driven by controller, as input sstables to it
live in maintenance set. Another reason is customization
of things like sstable origin, etc.
stop_sstable_writer() is extended because that's used by
regular_compaction to check for possibility of removing
exhausted sstables earlier whenever an output sstable
is sealed.
Also, incremental compaction will be unconditionally
enabled for ICS/LCS during off-strategy.

Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
2023-09-21 11:15:12 -03:00
Raphael S. Carvalho
33a0f42304 compaction: Move reshape_compaction in the source
That's in preparation to next change that will make reshape
inherit from regular compaction.

Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
2023-09-21 11:11:13 -03:00
Botond Dénes
a56a4b6226 Merge 'compaction_backlog_tracker: do not allow moving registered trackers' from Benny Halevy
Currently, the moved-object's manager pointer is moved into the
constructed object, but without fixing the registration to
point to the moved-to object, causing #15248.

Although we could properly move the registration from
the moved-from object to the moved-to one, it is simpler
to just disallow moving a registered tracker, since it's
not needed anywhere. This way we just don't need to mess
with the trackers' registration.

The move-assignment operator has a similar problem,
therefore it is deleted in this series, and the function is
renamed to `transfer_backlog` that just doesn't deal with the
moved-from registration.  This is safe since it's only used internally
by the compaction manager.

Fixes #15248

Closes scylladb/scylladb#15445

* github.com:scylladb/scylladb:
  compaction_state: store backlog_track in std::optional
  compaction_backlog_tracker: do not allow moving registered trackers
2023-09-20 16:41:10 +03:00
Botond Dénes
45dfce6632 Merge 'compaction: change behaviour of compaction task executors' from Aleksandra Martyniuk
Compaction tasks executors serve two different purposes - as compaction
manager related entity they execute compaction operation and as task
manager related entity they track compaction status.

When one role depends on the other, as it currently is for
compaction_task_impl::done() and compaction_task_executor::compaction_done(),
requirements of both roles need to be satisfied at the same time in each
corner case. Such complexity leads to bugs.

To prevent it, compaction_task_impl::done() of executors no longer depends
on compaction_task_executor::compaction_done().

Fixes: #14912.

Closes scylladb/scylladb#15140

* github.com:scylladb/scylladb:
  compaction: warn about compaction_done()
  compaction: do not run stopped compaction
  compaction: modify lowest compaction tasks' run method
  compaction: pass do_throw_if_stopping to compaction_task_executor
2023-09-19 15:15:14 +03:00
Benny Halevy
7ca91d719c compaction_state: store backlog_track in std::optional
So that replacing it will destroy the previous tracker
and unregister it before assigning the new one and
then registering it.

This is safer than assiging it in place.

With that, the move assignment operator is not longer
used and can be deleted.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
2023-09-19 13:59:54 +03:00
Benny Halevy
4ad4b632b8 compaction_backlog_tracker: do not allow moving registered trackers
Currently, the moved-object's manager pointer is moved into the
constructed object, but without fixing the registration to
point to the moved-to object, causing #15248.

Although we could properly move the registration from
the moved-from object to the moved-to one, it is simpler
to just disallow moving a registered tracker, since it's
not needed anywhere. This way we just don't need to mess
with the trackers' registration.

With that in mind, when move-assigning a compaction_backlog_tracker
the existing tracker can remain registered.

Fixes scylladb/scylladb#15248

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
2023-09-19 13:24:36 +03:00
Raphael S. Carvalho
6cc85068d7 compaction: Enable incremental compaction only if replacer callback is engaged
That's needed for enabling incremental compaction to operate, and
needed for subsequent work that enables incremental compaction
for off-strategy, which in turn uses reshape compaction type.

Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
2023-09-18 17:57:11 -03:00
Aleksandra Martyniuk
53ecc29cd7 compaction: unify exception messages
Use fmt::format in exception messages in all methods validating
compaction strategies.
2023-09-13 16:59:40 +02:00
Aleksandra Martyniuk
ac08b57555 compaction: cql3: validate options in check_restricted_table_properties
Check whether valid compaction strategy options are set for the given
strategy type in check_restricted_table_properties.
2023-09-13 16:59:40 +02:00
Aleksandra Martyniuk
44744d6229 compaction: validate options used in different compaction strategies
For each compaction strategy, validate whether options values are valid.
2023-09-13 16:59:40 +02:00
Aleksandra Martyniuk
0ed39af221 compaction: validate common compaction strategy options
Add compaction_strategy_impl::validate_options to validate common
compaction strategy options.
2023-09-13 16:59:40 +02:00
Aleksandra Martyniuk
a2e6081984 compaction: split compaction_strategy_impl constructor
Split compaction_strategy_impl constructor into methods that will
be reused for validation.

Add additional checks providing that options' values are legal.
2023-09-13 16:59:40 +02:00
Aleksandra Martyniuk
5c72bcd40e compaction: validate size_tiered_compaction_strategy specific options 2023-09-13 16:59:40 +02:00
Aleksandra Martyniuk
7e5b6ea09a compaction: validate time_window_compaction_strategy specific options 2023-09-13 16:59:40 +02:00
Aleksandra Martyniuk
84fd90e472 compaction: add method to validate min and max threshold
Add compaction_strategy_impl::validate_min_max_threshold method
that will be used to validate min and max threshold values
for different compaction methods.
2023-09-13 16:59:40 +02:00
Aleksandra Martyniuk
50c1bb555b compaction: split size_tiered_compaction_strategy_options constructor
Split size_tiered_compaction_strategy_options constructor into
methods that will be reused for validation.

Add additional checks providing that options' values are legal.
2023-09-13 16:59:40 +02:00
Aleksandra Martyniuk
702c19f941 compaction: make compaction strategy keys static constexpr 2023-09-13 16:59:40 +02:00
Aleksandra Martyniuk
e3d8f71a88 compaction: use helpers in validate_* functions
To be consistent with other compaction_strategy_options,
time_window_compaction_strategy_options uses compaction_strategy_impl::get_value
and cql3::statements::property_definitions::to_long helpers for
parsing.
2023-09-13 16:59:40 +02:00
Aleksandra Martyniuk
c8c3c0e6a6 compaction: split time_window_compaction_strategy_options construtor
Split time_window_compaction_strategy_options constructor into
functions that will be reused for validation.
2023-09-13 16:59:40 +02:00
Aleksandra Martyniuk
a01dd1351e compaction: add validate method to compaction_strategy_options
Add temporarily empty validate method to compaction_strategy_options.
The method will validate the options and help determining whether
only the allowed options were set.
2023-09-13 16:59:40 +02:00
Benny Halevy
e5cf6f0897 time_window_compaction_strategy_options: make copy and move-able
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
2023-09-13 16:59:40 +02:00
Benny Halevy
c9475d6fe0 size_tiered_compaction_strategy_options: make copy and move-able
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
2023-09-13 16:59:40 +02:00
Aleksandra Martyniuk
932f39e37c compaction: warn about compaction_done()
compaction_done() returns ready future before compaction_task_executor::run_compaction()
even though the compaction did not start.

Make compaction_done() private and add a comment to warn against
incorrect usage.
2023-09-09 11:19:11 +02:00
Aleksandra Martyniuk
59b7a45f73 compaction: do not run stopped compaction
Before compaction_task_executor::do_run	is called, the executor	can
be already aborted. Check if compaction	was stopped and set
_compaction_done to exceptional	future.
2023-09-09 11:19:11 +02:00
Aleksandra Martyniuk
515b8d4890 compaction: modify lowest compaction tasks' run method
For compaction_task_executors, unlike for all other task manager
tasks, run method does not embrace operations performed in a scope
of a task, but only waits until shared_future connected with
the operations is resolved.

Apart from breaking task manager task conventions, such a run method
must consider all corner cases, not to break task manager or
compaction manager functionality.

To fix existing and prevent further bugs related to task manager
and compaction manager coexistence, call perform_task inside
run method and wait for it in a standard way.

Executors that are not going to be reflected in task manager run call
perform_task the old way.
2023-09-09 11:19:11 +02:00
Aleksandra Martyniuk
832df38d26 compaction: pass do_throw_if_stopping to compaction_task_executor
As a preparation for further changes, keep do_throw_if_stopping flag
as a member of compaction_task_executor.
2023-09-09 11:19:11 +02:00
Benny Halevy
cfecb68245 compaction_manager: stop: close compaction_state:s gates
Make sure the compaction_state:s are idle before
they are destroyed. Although all tasks are stopped
in stop_ongoing_compactions, make sure there is
fiber holding the compaction_state gate.

compaction_manager::remove now needs to close the
compaction_state gate and to stop_ongoing_compactions
only if the gate is not closed yet.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
2023-09-05 09:17:25 +03:00
Benny Halevy
96055414c7 compaction_manager: gracefully handle gate close
Check if the compaction_state gate is closed
along with _state != state::enabled and return early
in this case.

At this point entering the gate is guaranteed to succeed.
So enter the gate before calling `perform_compaction`
keeping the std::optional<gate_holder> throughout
the compaction task.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
2023-09-05 09:17:25 +03:00
Aleksandra Martyniuk
5e31ca7d20 tasks: api: show tasks' scopes
To make manual analysis of task manager tasks easier, task_status
and task_stats contain operation scope (e.g. shard, table).

Closes #15172
2023-08-29 11:32:16 +03:00
Botond Dénes
1609c76d62 tools/scylla-sstable: scrub: don't qurantine sstables after validate
Scylla sstable promises to *never* mutate its input sstables. This
promise was broken by `scylla sstable scrub --scrub-mode=validate`,
because validate moves invalid input sstables into qurantine. This is
unexpected and caused occasional failures in the scrub tests in
test_tools.py. Fix by propagating a flag down to
`scrub_sstables_validate_mode()` in `compaction.cc`, specifying whether
validate should qurantine invalid sstables, then set this flag to false
in `scylla-sstable.cc`. The existing test for validate-mode scrub is
ammended to check that the sstable is not mutated. The test now fails
before the fix and passes afterwards.

Fixes: #14309

Closes #15139
2023-08-23 21:53:12 +03:00
Aleksandra Martyniuk
e0ce711e4f compaction: do not swallow compaction_stopped_exception for reshape
Loop in shard_reshaping_compaction_task_impl::run relies on whether
sstables::compaction_stopped_exception is thrown from run_custom_job.
The exception is swallowed for each type of compaction
in compaction_manager::perform_task.

Rethrow an exception in perfrom task for reshape compaction.

Fixes: #15058.

Closes #15067
2023-08-21 12:41:55 +03:00
Tomasz Grabiec
bd8bb5d4b1 Merge 'Wire tablet into compaction group' from Raphael "Raph" Carvalho
Compaction group is the data plane for tablets, so this integration
allows each tablet to have its own storage (memtable + sstables).
A crucial step for dynamic tablets, where each tablet can be worked
on independently.

There are still some inefficiencies to be worked on, but as it is,
it already unlocks further development.

```
INFO  2023-07-27 22:43:38,331 [shard 0] init - loading tablet metadata
INFO  2023-07-27 22:43:38,333 [shard 0] init - loading non-system sstables
INFO  2023-07-27 22:43:38,354 [shard 0] table - Tablet with id 0 present for ks.cf
INFO  2023-07-27 22:43:38,354 [shard 0] table - Tablet with id 2 present for ks.cf
INFO  2023-07-27 22:43:38,354 [shard 0] table - Tablet with id 4 present for ks.cf
INFO  2023-07-27 22:43:38,354 [shard 0] table - Tablet with id 6 present for ks.cf
INFO  2023-07-27 22:43:38,428 [shard 1] table - Tablet with id 1 present for ks.cf
INFO  2023-07-27 22:43:38,428 [shard 1] table - Tablet with id 3 present for ks.cf
INFO  2023-07-27 22:43:38,428 [shard 1] table - Tablet with id 5 present for ks.cf
INFO  2023-07-27 22:43:38,428 [shard 1] table - Tablet with id 7 present for ks.cf
```

Closes #14863

* github.com:scylladb/scylladb:
  Kill scylla option to configure number of compaction groups
  replica: Wire tablet into compaction group
  token_metadata: Add this_host_id to topology config
  replica: Switch to chunked_vector for storing compaction groups
  replica: Generate group_id for compaction_group on demand
2023-08-18 15:17:17 +02:00
Aleksandra Martyniuk
e9d94894f1 compaction: release resources of compaction executors
Before compaction task executors started inheriting from
compaction_task_impl, they were destructed immediately after
compaction finished. Destructors of executors and their
fields performed actions that affected global structures and
statistics and had impact on compaction process.

Currently, task executors are kept in memory much longer, as their
are tracked by task manager. Thus, destructors are not called just
after the compaction, which results in compaction stats not being
updated, which causes e.g. infinite cleanup loop.

Add release_resources() method which is called at the end
of compaction process and does what destructors used to.

Fixes: #14966.
Fixes: #15030.

Closes #15005
2023-08-16 15:51:17 +03:00
Avi Kivity
e8f3b073c3 Merge 'Maintain sstable state explicitly' from Pavel Emelyanov
An sstable can be in one of several states -- normal, quarantined, staging, uploading. Right now this "state" is hard-wired into sstable's path, e.g. quarantined sstable would sit in e.g. /var/lib/data/ks-cf-012345/quarantine/ directory. Respectively, there's a bunch of directory names constexprs in sstables.hh defining each "state". Other than being confusing, this approach doesn't work well with S3 backend. Additionally, there's snapshot subdir that adds to the confusion, because snapshot is not quite a state.

This PR converts "state" from constexpr char* directories names into a enum class and patches the sstable creation, opening and state-changing API to use that enum instead of parsing the path.

refs: #13017
refs: #12707

Closes #14152

* github.com:scylladb/scylladb:
  sstable/storage: Make filesystem storage with initial state
  sstable: Maintain state
  sstable: Make .change_state() accept state, not directory string
  sstable: Construct it with state
  sstables_manager: Remove state-less make_sstable()
  table: Make sstables with required state
  test: Make sstables with upload state in some cases
  tools: Make sstables with normal state
  table: Open-code sstables making streaming helpers
  tests: Make sstables with normal state by default
  sstable_directory: Make sstable with required state
  sstable_directory: Construct with state
  distributed_loader: Make sstable with desired state when populating
  distributed_loader: Make sstable with upload state when uploading
  sstable: Introduce state enum
  sstable_directory: Merge verify and g.c. calls
  distributed_loader: Merge verify and gc invocations
  sstable/filesystem: Put underscores to dir members
  sstable/s3: Mark make_s3_object_name() const
  sstable: Remove filename(dir, ...) method
2023-08-15 17:44:06 +03:00
Raphael S. Carvalho
2590eec352 replica: Generate group_id for compaction_group on demand
There are a few good reasons for this change.
1) compaction_group doesn't have to be aware of # of groups
2) thinking forward to dynamic tablets, # of groups cannot be
statically embedded in group id, otherwise it gets stale.

Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
2023-08-15 09:04:05 -03:00
Benny Halevy
9f77a32805 compaction_manager: run_offstrategy_compaction: retrieve owned_ranges from compaction_state
perform_offstrategy is called from try_perform_cleanup
when there are sstables in the maintenance set that require
cleanup.

The input sstables are inserted into the compaction_state
`sstables_requiring_cleanup` and `try_perform_cleanup`
expects offstrategy compaction to clean them up along
with reshape compaction.

Otherwise, the maintenance sstables that require cleanup
are not cleaned up by cleanup compaction, since
the reshape output sstable(s) are not analyzed again
after reshape compaction, where that would insert
the output sstable(s) into `sstables_requiring_cleanup`
and trigger their cleanup in the subsequent cleanup compaction.

The latter method is viable too, but it is less effficient
since we can do reshape+cleanup in one pass, vs.
reshape first and cleanup later.

Fixes scylladb/scylladb#15041

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>

Closes #15043
2023-08-14 18:37:34 +03:00
Aleksandra Martyniuk
7a28cc60ec compaction: ignore future explicitly
discard_result ignores only successful futures. Thus, if
perform_compaction<regular_compaction_task_executor> call fails,
a failure is considered abandoned, causing tests to fail.

Explicitly ignore failed future.

Fixes: #14971.

Closes #15000
2023-08-14 16:41:15 +03:00
Pavel Emelyanov
b06917f235 sstable: Make .change_state() accept state, not directory string
Pretty cosmetic change, but it will allow S3 to finally support moving
sstables between states (after this patch it still doesn't)

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
2023-08-14 15:40:44 +03:00
Aleksandra Martyniuk
9ec43fd3a7 compaction: update comment in compaction_manager::submit
Closes #15023
2023-08-14 09:34:56 +03:00
Aleksandra Martyniuk
db932c7106 compaction: hold gate immediately after task executor is created
If make_task call in compaction_manager::perform_compaction yields,
compaction_task_executor::_compaction_state may be gone and gate
won't be held.

Hold gate immediately after compaction_task_executor is created.
Add comment not to call prepare_task without preparation.

Refs: #14971.
Fixes: #14977.

Closes #14999
2023-08-11 13:56:38 +02:00