Unlike flat_mutation_reader_opt that is defined using
optimized_optional<flat_mutation_reader>, std::optional<T> does not evaluate
to `false` after being moved, only after it is explicitly reset.
Use flat_mutation_reader_opt rather than std::optional<flat_mutation_reader>
to make it easier to check if it was closed before it's destroyed
or being assigned-over.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
Message-Id: <20210215101254.480228-6-bhalevy@scylladb.com>
The main motivation for this patchset is to prepare
for adding a async close() method to flat_mutation_reader.
In order to close the reader before destroying it
in all paths we need to make next_partition asynchronous
so it can asynchronously close a current reader before
destoring it, e.g. by reassignment of flat_mutation_reader_opt,
as done in scanning_reader::next_partition.
Test: unit(release, debug)
* git@github.com:bhalevy/scylla.git futurize-next-partition-v1:
flat_mutation_reader: return future from next_partition
multishard_mutation_query: read_context: save_reader: destroy reader_meta from the calling shard
mutation_reader: filtering_reader: fill_buffer: futurize inner loop
flat_mutation_reader::impl: consumer_adapter: futurize handle_result
flat_mutation_reader: consume_pausable/in_thread: futurize_invoke consumer
flat_mutation_reader: FlatMutationReaderConsumer: support also async consumer
flat_mutation_reader:impl: get rid of _consume_done member
This is a revival of #7490.
Quoting #7490:
The managed_bytes class now uses implicit linearization: outside LSA, data is never fragmented, and within LSA, data is linearized on-demand, as long as the code is running within with_linearized_managed_bytes() scope.
We would like to stop linearizing managed_bytes and keep it fragmented at all times, since linearization can require large contiguous chunks. Large contiguous allocations are hard to satisfy and cause latency spikes.
As a first step towards that, we remove all implicitly linearizing accessors and replace them with an explicit linearization accessor, with_linearized().
Some of the linearization happens long before use, by creating a bytes_view of the managed_bytes object and passing it onwards, perhaps storing it for later use. This does not work with with_linearized(), which creates a temporary linearized view, and does not work towards the longer term goal of never linearizing. As a substitute a managed_bytes_view class is introduced that acts as a view for managed_bytes (for interoperability it can also be a view for bytes and is compatible with bytes_view).
By the end of the series, all linearizations are temporary, within the scope of a with_linearized() call and can be converted to fragmented consumption of the data at leisure.
This has limited practical value directly, as current uses of managed_bytes are limited to keys (which are limited to 64k). However, it enables converting the atomic_cell layer back to managed_bytes (so we can remove IMR) and the CQL layer to managed_bytes/managed_bytes_view, removing contiguous allocations from the coordinator.
Closes#7820
* github.com:scylladb/scylla:
test: add hashers_test
memtable: fix accounting of managed_bytes in partition_snapshot_accounter
test: add managed_bytes_test
utils: fragment_range: add a fragment iterator for FragmentedView
keys: update comments after changes and remove an unused method
mutation_test: use the correct preferred_max_contiguous_allocation in measuring_allocator
row_cache: more indentation fixes
utils: remove unused linearization facilities in `managed_bytes` class
misc: fix indentation
treewide: remove remaining `with_linearized_managed_bytes` uses
memtable, row_cache: remove `with_linearized_managed_bytes` uses
utils: managed_bytes: remove linearizing accessors
keys, compound: switch from bytes_view to managed_bytes_view
sstables: writer: add write_* helpers for managed_bytes_view
compound_compat: transition legacy_compound_view from bytes_view to managed_bytes_view
types: change equal() to accept managed_bytes_view
types: add parallel interfaces for managed_bytes_view
types: add to_managed_bytes(const sstring&)
serializer_impl: handle managed_bytes without linearizing
utils: managed_bytes: add managed_bytes_view::operator[]
utils: managed_bytes: introduce managed_bytes_view
utils: fragment_range: add serialization helpers for FragmentedMutableView
bytes: implement std::hash using appending_hash
utils: mutable_view: add substr()
utils: fragment_range: add compare_unsigned
utils: managed_bytes: make the constructors from bytes and bytes_view explicit
utils: managed_bytes: introduce with_linearized()
utils: managed_bytes: constrain with_linearized_managed_bytes()
utils: managed_bytes: avoid internal uses of managed_bytes::data()
utils: managed_bytes: extract do_linearize_pure()
thrift: do not depend on implicit conversion of keys to bytes_view
clustering_bounds_comparator: do not depend on implicit conversion of keys to bytes_view
cql3: expression: linearize get_value_from_mutation() eariler
bytes: add to_bytes(bytes)
cql3: expression: mark do_get_value() as static
managed_bytes has a small overhead per each fragment. Due to that, managed_bytes
containing the same data can have different total memory usage in different
allocators. The smaller the preferred max allocation size setting is, the more
fragments are needed and the greater total per-fragment overhead is.
In particular, managed_bytes allocated in the LSA could grow in
memory usage when copied to the standard allocator, if the standard allocator
had a preferred max allocation setting smaller than the LSA.
partition_snapshot_accounter calculates the amount of memory used by
mutation fragments in the memtable (where they are allocated with LSA) based
on the memory usage after they are copied to the standard allocator.
This could result in an overestimation, as explained above.
But partition_snapshot_accounter must not overestimate the amount of freed
memory, as doing otherwise might result in OOM situations.
This patch prevents the overaccounting by adding minimal_external_memory_usage():
a new version of external_memory_usage(), which ignores allocator-dependent
overhead. In particular, it includes the per-fragment overhead in managed_bytes
only once, no matter how many fragments there are.
The patch fixes indentation issues introduced in previous patches
related to removing `with_linearized_managed_bytes` uses from the
code tree.
Signed-off-by: Pavel Solodovnikov <pa.solodovnikov@scylladb.com>
Since `managed_bytes::data()` is deleted as well as other public
APIs of `managed_bytes` which would linearize stored values except
for explicit `with_linearized`, there is no point
invoking `with_linearized_managed_bytes` hack which would trigger
automatic linearization under the hood of managed_bytes.
Remove useless `with_linearized_managed_bytes` wrapper from
memtable and row_cache code.
Signed-off-by: Pavel Solodovnikov <pa.solodovnikov@scylladb.com>
Tracking both min and max timestamp will be required for memtable flush
to short-circuit interposer consumer if needed.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Require a schema and an operation name to be given to each permit when
created. The schema is of the table the read is executed against, and
the operation name, which is some name identifying the operation the
permit is part of. Ideally this should be different for each site the
permit is created at, to be able to discern not only different kind of
reads, but different code paths the read took.
As not all read can be associated with one schema, the schema is allowed
to be null.
The name will be used for debugging purposes, both for coredump
debugging and runtime logging of permit-related diagnostics.
The main user of this method, the one which required this method to
return the collective buffer size of the entire reader tree, is now
gone. The remaining two users just use it to check the size of the
reader instance they are working with.
So de-virtualize this method and reduce its responsibility to just
returning the buffer size of the current reader instance.
Not used yet, this patch does all the churn of propagating a permit
to each impl.
In the next patch we will use it to track to track the memory
consumption of `_buffer`.
The change is the same as with row-cache -- use B+ with int64_t token
as key and array of memtable_entry-s inside it.
The changes are:
Similar to those for row_cache:
- compare() goes away, new collection uses ring_position_comparator
- insertion and removal happens with the help of double_decker, most
of the places are about slightly changed semantics of it
- flags are added to memtable_entry, this makes its size larger than
it could be, but still smaller than it was before
Memtable-specific:
- when the new entry is inserted into tree iterators _might_ get
invalidated by double-decker inner array. This is easy to check
when it happens, so the invalidation is avoided when possible
- the size_in_allocator_without_rows() is now not very precise. This
is because after the patch memtable_entries are not allocated
individually as they used to. They can be squashed together with
those having token conflict and asking allocator for the occupied
memory slot is not possible. As the closest (lower) estimate the
size of enclosing B+ data node is used
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
All reader are soon going to require a valid permit, so make sure we
have a valid permit which we can pass to the delegate reader when
creating it. This means `memtable::make_flat_reader()` now also requires
a permit to be passed to it.
Internally the permit is stored in `scanning_reader`, which is used both
for flushes and normal reads. In the former case a permit is not
required.
We typically use `std::bad_function_call` to throw from
mandatory-to-implement virtual functions, that cannot have a meaningful
implementation in the derived class. The problem with
`std::bad_function_call` is that it carries absolutely no information
w.r.t. where was it thrown from.
I originally wanted to replace `std::bad_function_call` in our codebase
with a custom exception type that would allow passing in the name of the
function it is thrown from to be included in the exception message.
However after I ended up also including a backtrace, Benny Halevy
pointed out that I might as well just throw `std:bad_function_call` with
a backtrace instead. So this is what this patch does.
All users are various unimplemented methods of the
`flat_mutation_reader::impl` interface.
Signed-off-by: Botond Dénes <bdenes@scylladb.com>
Message-Id: <20200408075801.701416-1-bdenes@scylladb.com>
and replace all dht::global_partitioner().decorate_key
with dht::decorate_key
It is an improvement because dht::decorate_key takes schema
and uses it to obtain partitioner instead of using global
partitioner as it was before.
Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>
The former was never really more than a reader_permit with one
additional method. Currently using it doesn't even save one from any
includes. Now that readers will be using reader_permit we would have to
pass down both to mutation_source. Instead get rid of
reader_resource_tracker and just use reader_permit. Instead of making it
a last and optional parameter that is easy to ignore, make it a
first class parameter, right after schema, to signify that permits are
now a prominent part of the reader API.
This -- mostly mechanical -- patch essentially refactors mutation_source
to ask for the reader_permit instead of reader_resource_tracking and
updates all usage sites.
Adds per-table metrics for counting partition and row reuse
in memtables. New metrics are as follows:
- memtable_partition_writes - number of write operations performed
on partitions in memtables,
- memtable_partition_hits - number of write operations performed
on partitions that previously existed in a memtable,
- memtable_row_writes - number of row write operations performed
in memtables,
- memtable_row_hits - number of row write operations that ovewrote
rows previously present in a memtable.
Tests: unit(release)
`collection_type_impl::serialize_mutation_form`
became `collection_mutation(_view)_description::serialize`.
Previously callers had to cast their data_type down to collection_type
to use serialize_mutation_form. Now it's done inside `serialize`.
In the future `serialize` will be generalized to handle UDTs.
`collection_type_impl::deserialize_mutation_form`
became a free standing function `deserialize_collection_mutation`
with similiar benefits. Actually, noone needs to call this function
manually because of the next paragraph.
A common pattern consisting of linearizing data inside a `collection_mutation_view`
followed by calling `deserialize_mutation_form` has been abstracted out
as a `with_deserialized` method inside collection_mutation_view.
serialize_mutation_form_only_live was removed,
because it hadn't been used anywhere.
Merged patch series from Avi Kivity:
The static row can be rare: many tables don't have them, and tables
that do will often have mutations without them (if the static row
is rarely updated, it may be present in the cache and in readers,
but absent in memtable mutations). However, it always consumes ~100
bytes of memory, even if it not present, due to row's overhead.
Change it to be optional by allocating it as an external object rather
than inlined into mutation_partition. This adds overhead when the
static row is present (17 bytes for the reference, back reference,
and lsa allocator overhead).
perf_simple_query appears to marginally (2%) faster. Footprint is
reduced by ~9% for a cache entry, 12% in memtables. More details are
provided in the patch commitlog.
Tests: unit (debug)
Avi Kivity (4):
managed_ref: add get() accessor
managed_ref: add external_memory_usage()
mutation_partition: introduce lazy_row
mutation_partition: make static_row optional to reduce memory
footprint
cell_locking.hh | 2 +-
converting_mutation_partition_applier.hh | 4 +-
mutation_partition.hh | 284 ++++++++++++++++++++++-
partition_builder.hh | 4 +-
utils/managed_ref.hh | 12 +
flat_mutation_reader.cc | 2 +-
memtable.cc | 2 +-
mutation_partition.cc | 45 +++-
mutation_partition_serializer.cc | 2 +-
partition_version.cc | 4 +-
tests/multishard_mutation_query_test.cc | 2 +-
tests/mutation_source_test.cc | 2 +-
tests/mutation_test.cc | 12 +-
tests/sstable_mutation_test.cc | 10 +-
14 files changed, 355 insertions(+), 32 deletions(-)
The static row can be rare: many tables don't have them, and tables
that do will often have mutations without them (if the static row
is rarely updated, it may be present in the cache and in readers,
but absent in memtable mutations). However, it always consumes ~100
bytes of memory, even if it not present, due to row's overhead.
Change it to be optional by using lazy_row instead of row. Some call
sites treewide were adjusted to deal with the extra indirection.
perf_simple_query appears to improve by 2%, from 163krps to 165 krps,
though it's hard to be sure due to noisy measurements.
memory_footprint comparisons (before/after):
mutation footprint: mutation footprint:
- in cache: 1096 - in cache: 992
- in memtable: 854 - in memtable: 750
- in sstable: 351 - in sstable: 351
- frozen: 540 - frozen: 540
- canonical: 827 - canonical: 827
- query result: 342 - query result: 342
sizeof(cache_entry) = 112 sizeof(cache_entry) = 112
-- sizeof(decorated_key) = 36 -- sizeof(decorated_key) = 36
-- sizeof(cache_link_type) = 32 -- sizeof(cache_link_type) = 32
-- sizeof(mutation_partition) = 200 -- sizeof(mutation_partition) = 96
-- -- sizeof(_static_row) = 112 -- -- sizeof(_static_row) = 8
-- -- sizeof(_rows) = 24 -- -- sizeof(_rows) = 24
-- -- sizeof(_row_tombstones) = 40 -- -- sizeof(_row_tombstones) = 40
sizeof(rows_entry) = 232 sizeof(rows_entry) = 232
sizeof(lru_link_type) = 16 sizeof(lru_link_type) = 16
sizeof(deletable_row) = 168 sizeof(deletable_row) = 168
sizeof(row) = 112 sizeof(row) = 112
sizeof(atomic_cell_or_collection) = 8 sizeof(atomic_cell_or_collection) = 8
Tests: unit (dev)
Replace stdx::optional and stdx::string_view with the C++ std
counterparts.
Some instances of boost::variant were also replaced with std::variant,
namely those that called seastar::visit.
Scylla now requires GCC 8 to compile.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
Message-Id: <20190108111141.5369-1-duarte@scylladb.com>
Single-partition reader is less expensive than the one that accepts any
range of partitions, but it doesn't support fast-forwarding to another
partition range properly and therefore cannot be used if that option is
enabled.
After the new in-memory representation of cells was introduced there was
a regression in atomic_cell_or_collection::operator<< which stopped
printing the content of the cell. This makes debugging more incovenient
are time-consuming. This patch fixes the problem. Schema is propagated
to the atomic_cell_or_collection printer and the full content of the
cell is printed.
Fixes#3571.
Message-Id: <20181024095413.10736-1-pdziepak@scylladb.com>
Currently timeout is opt-in, that is, all methods that even have it
default it to `db::no_timeout`. This means that ensuring timeout is used
where it should be is completely up to the author and the reviewrs of
the code. As humans are notoriously prone to mistakes this has resulted
in a very inconsistent usage of timeout, many clients of
`flat_mutation_reader` passing the timeout only to some members and only
on certain call sites. This is small wonder considering that some core
operations like `operator()()` only recently received a timeout
parameter and others like `peek()` didn't even have one until this
patch. Both of these methods call `fill_buffer()` which potentially
talks to the lower layers and is supposed to propagate the timeout.
All this makes the `flat_mutation_reader`'s timeout effectively useless.
To make order in this chaos make the timeout parameter a mandatory one
on all `flat_mutation_reader` methods that need it. This ensures that
humans now get a reminder from the compiler when they forget to pass the
timeout. Clients can still opt-out from passing a timeout by passing
`db::no_timeout` (the previous default value) but this will be now
explicit and developers should think before typing it.
There were suprisingly few core call sites to fix up. Where a timeout
was available nearby I propagated it to be able to pass it to the
reader, where I couldn't I passed `db::no_timeout`. Authors of the
latter kind of code (view, streaming and repair are some of the notable
examples) should maybe consider propagating down a timeout if needed.
In the test code (the wast majority of the changes) I just used
`db::no_timeout` everywhere.
Tests: unit(release, debug)
Signed-off-by: Botond Dénes <bdenes@scylladb.com>
Message-Id: <1edc10802d5eb23de8af28c9f48b8d3be0f1a468.1536744563.git.bdenes@scylladb.com>
boost::intrusive::set::insert() may throw if keys require
linearization and that fails, in which case we will leak the entry.
When this happens in cache, we will also violate the invariant for
entry eviction, which assumes all tracked entries are linked, and
cause a SEGFAULT.
Use the non-throwing and faster insert_before() instead. Where we
can't use insert_before(), use alloc_strategy_unique_ptr<> to ensure
that entry is deallocated on insert failure.
Fixes#3585.
The worker is responsible for merging MVCC snapshots, which is similar
to merging sstables, but in memory. The new scheduling group will be
therefore called "memory compaction".
We should run it in a separate scheduling group instead of
main/memtables, so that it doesn't disrupt writes and other system
activities. It's also nice for monitoring how much CPU time we spend
on this.
If memtable snapshot goes away after memtable started merging to
cache, it would enqueue the snapshots for cleaning on the memtable's
cleaner, which will have to clean without deferrring when the memtable
is destroyed. That may stall the reactor. To avoid this, make merge()
cause the old instance of the cleaner to redirect to the new instance
(owned by cache), like we do for regions. This way the snapshots
mentioned earlier can be cleaned after memtable is destroyed,
gracefully.
Before this patch, maybe_merge_versions() had to be manually called
before partition snapshot goes away. That is error prone and makes
client code more complicated. Delegate that task to a new
partition_snapshot_ptr object, through which all snapshots are
published now.
Now all snapshots will have a mutation_cleaner which they will use to
gently destroy freed partition_version objects.
Destruction of memtable entries during cache update is also using the
gentle cleaner now. We need to have a separate cleaner for memtable
objects even though they're owned by cache's region, because memtable
versions must be cleared without a cache_tracker.
Each memtable will have its own cleaner, which will be merged with the
cache's cleaner when memtable is merged into cache.
Fixes some sources of reactor stalls on cache update when there are
large partition entries in memtables.
Partitions can get very large. Destroying them all at once can stall
the reactor for significant amount of time. We want to avoid that by
doing destruction incrementally, deferring in between. A new API is
added for that at various levels:
stop_iteration clear_gently() noexcept;
It returns stop_iteration::yes when the object is fully cleared and
can be now destroyed quickly. So a deferring destruction can look like
this:
return repeat([this] { return clear_gently(); });
The reason why clear_gently() doesn't return a future<> itself is that some
contexts cannot defer, like memory reclamation.
We keep track of all updates and store the minimal values of timestamps,
TTLs and local deletion times across all the inserted data.
These values are written as a part of serialization_header for
Statistics.db and used for delta-encoding values when writing Data.db
file in SSTables 3.0 (mc) format.
For #1969.
Signed-off-by: Vladimir Krivopalov <vladimir@scylladb.com>
Previously it was also possible to pass a frozen_mutation to it.
Now we de-serialize frozen mutations at the calling side.
This is a pre-requisite for collecting memtable statistics needed for
writing into the SSTables 3.0 format.
For #1969.
Signed-off-by: Vladimir Krivopalov <vladimir@scylladb.com>
buffer_size() exposes the collective size of the external memory
consumed by the mutattion-fragments in the flat reader's buffer. This
provides a basis to build basic memory accounting on. Altought this is
not the entire memory consumption of any given reader it is the most
volatile component and usually by far the largest one too.
In this patchset I am resubmitting Avi's enablement of the CPU scheduler
in his behalf. I've done a ton of testing in the series and there are
some improvements / changes that I had previously sent as a separate series.
What you see here is the result of merging that work.
After this patchset is applied, workloads are smoother and we are able to
uphold the pre-defined shares among the various actors.
We also finally have everything we need to merge the CPU and I/O controllers.
After that is done the code is now much simpler. But also, as a bonus,
controllers that were previously available for I/O only (compactions) are
enabled for CPU as well.
* git@github.com:glommer/scylla.git cpusched-v7:
Avi Kivity (4):
database, sstables, compaction: convert use of thread_scheduling_group
to seastar cpu scheduler
memtable, database: make memtable::clear_gently() inherit
scheduling_group
config: mark background_writer_scheduling_quota as Unused
database: place data_query execution stage into scheduling_group
Glauber Costa (9):
database, main: set up scheduling_groups for our main tasks
row_cache: actually use the scheduling group for update_cache
allow update_cache and clear_gently to use the entire task quota.
database: remove cpu_flush_quota metric
controllers: retire auto_adjust_flush_quota
controllers: allow memtable I/O controller to have shares statically
set
controllers: update control points for memtable I/O controller
controllers: allow a static priority to override the controller output
controllers: unify the I/O and CPU controllers
We have had a quota of partitions to process in clear_gently /
update_cache, so that we don't overwork. However, with those things now
being in their own task group there is no harm in allowing it to run
until we reach a natural preemption point.
While we are at it, clear_gently did not check for need_preempt()
before, so this patch fixes it.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
