Currently, the sstable_set in a table is copied before every change
to allow accessing the unchanged version by existing sstable readers.
This patch changes the sstable_set to a structure that keeps all its
versions that are referenced somewhere and provides a way of getting
a reference to an immutable version of the set.
Each sstable in the set is associated with the versions it is alive in,
and is removed when all such versions don't have references anymore.
To avoid copying, the object holding all sstables in the set version is
changed to a new structure, sstable_list, which was previously an alias
for std::unordered_set<shared_sstable>, and which implements most of the
methods of an unordered_set, but its iterator uses the actual set with
all sstables from all referenced versions and iterates over those
sstables that belong to the captured version.
The methods that modify the sets contents give strong exception guarantee
by trying to insert new sstables to its containers, and erasing them in
the case of an caught exception.
To release shared_sstables as soon as possible (i.e. when all references
to versions that contain them die), each time a version is removed, all
sstables that were referenced exclusively by this version are erased. We
are able to find these sstables efficiently by storing, for each version,
all sstables that were added and erased in it, and, when a version is
removed, merging it with the next one. When a version that adds an sstable
gets merged with a version that removes it, this sstable is erased.
Fixes#2622
Signed-off-by: Wojciech Mitros wojciech.mitros@scylladb.comCloses#8111
* github.com:scylladb/scylla:
sstables: add test for checking the latency of updating the sstable_set in a table
sstables: move column_family_test class from test/boost to test/lib
sstables: use fast copying of the sstable_set instead of rebuilding it
sstables: replace the sstable_set with a versioned structure
sstables: remove potential ub
sstables: make sstable_set constructor less error-prone
fill_buffer() will keep scanning until _lower_bound_changed is true,
even if preemption is signaled, so that the reader makes forward
progress.
Before the patch, we did not update _lower_bound on touching a dummy
entry. The read will not respect preemption until we hit a non-dummy
row. If there is a lot of dummy rows, that can cause reactor stalls.
Fix that by updating _lower_bound on dummy entries as well.
Refs #8153.
Tested with perf_row_cache_reads:
```
$ build/release/test/perf/perf_row_cache_reads -c1 -m200M
Rows in cache: 0
Populating with dummy rows
Rows in cache: 373929
Scanning
read: 183.658966 [ms], preemption: {count: 848, 99%: 0.545791 [ms], max: 0.519343 [ms]}, cache: 99/100 [MB]
read: 120.951515 [ms], preemption: {count: 257, 99%: 0.545791 [ms], max: 0.518795 [ms]}, cache: 99/100 [MB]
```
Notice that max preemption latency is low in the second "read:" line.
Closes#8167
* github.com:scylladb/scylla:
row_cache: Make fill_buffer() preemptable when cursor leads with dummy rows
tests: perf: Introduce perf_row_cache_reads
row_cache: Add metric for dummy row hits
After switching cells storage onto compact radix tree it
becomes useful to know the tree nodes' sizes.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
In some places scylla clones collections of objects, so it's
sometimes needed to measure the speed of this operation.
This patch adds a placeholder for it, but no implementations
for any supported collections. It will be added soon for radix
tree.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
The --column-count makes the test generate schema with
the given numbers of columns and make mutation maker
fill random column with the value on each iteration.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Teach the schema builder and test itself to work on more
than one regular column, but for now only use 1, as before.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Added a test which measures the time it takes to replace sstables in a table's
sstable_set, using the leveled compaction strategy.
Signed-off-by: Wojciech Mitros <wojciech.mitros@scylladb.com>
After the switch from BST to B-tree the memory foorprint includes inner/leaf nodes
from the B-tree, so it's useful to know their sizes too.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
The design of the tree goes from the row-cache needs, which are
1. Insert/Remove do not invalidate iterators
2. Elements are LSA-manageable
3. Low key overhead
4. External tri-comparator
5. As little actions on insert/remove as possible
With the above the design is
Two types of nodes -- inner and leaf. Both types keep pointer on parent nodes
and N pointers on keys (not keys themselves). Two differences: inner nodes have
array of pointers on kids, leaf nodes keep pointer on the tree (to update left-
and rightmost tree pointers on node move).
Nodes do not keep pointers/references on trees, thus we have O(1) move of any
object, but O(logN) to get the tree size. Fortunately, with big keys-per-node
value this won't result in too many steps.
In turn, the tree has 3 pointers -- root, left- and rightmost leaves. The latter
is for constant-time begin() and end().
Keys are managed by user with the help of embeddable member_hook instance,
which is 1 pointer in size.
The code was copied from the B+ tree one, then heavily reworked, the internal
algorythms turned out to differ quite significantly.
For the sake of mutation_partition::apply_monotonically(), which needs to move
an element from one tree into another, there's a key_grabber helping wrapper
that allows doing this move respecting the exception-safety requirement.
As measured by the perf_collections test the B-tree with 8 keys is faster, than
the std::set, but slower than the B+tree:
vs set vs b+tree
fill: +13% -6%
find: +23% -35%
Another neat thing is that 1-key insertion-removal is ~40% faster than
for BST (the same number of allocations, but the key object is smaller,
less pointers to set-up and less instructions to execute when linking
node with root).
v4:
- equip insertion methods with on_alloc_point() calls to catch
potential exception guarantees violations eariler
- add unlink_leftmost_without_rebalance. The method is borrowed from
boost intrusive set, and is added to kill two birds -- provide it,
as it turns out to be popular, and use a bit faster step-by-step
tree destruction than plain begin+erase loop
v3:
- introduce "inline" root node that is embedded into tree object and in
which the 1st key is inserted. This greatly improves the 1-key-tree
performance, which is pretty common case for rows cache
v2:
- introduce "linear" root leaf that grows on demand
This improves the memory consumption for small trees. This linear node may
and should over-grow the NodeSize parameter. This comes from the fact that
there are two big per-key memory spikes on small trees -- 1-key root leaf
and the first split, when the tree becomes 1-key root with two half-filled
leaves. If the linear extention goes above NodeSize it can flatten even the
2nd peak
- mitigate the keys indirection a bit
Prefetching the keys while doing the intra-node linear scan and the nodes
while descending the tree gives ~+5% of fill and find
- generalize stress tests for B and B+ trees
- cosmetic changes
TODO:
- fix few inefficincies in the core code (walks the sub-tree twice sometimes)
- try to optimize the leaf nodes, that are not lef-/righmost not to carry
unused tree pointer on board
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
"
Currently there are three different methods for creating an sstable
reader:
* one for single key reads
* one for ranged reads
* and one nobody uses
This patch-set consolidates all these into a single `make_reader()`
method, which behind the scenes uses the same logic to dispatch to the
right sstable reader constructor that `sstables::as_mutation_source()`
uses.
This patch-set is part of an effort to clean up the jungle that is the
various reader creation methods. The next step is to clean up the
sstable_set, which has even more methods.
One very sad discovery I made while working on this patch-set is that
we
still default `mutation_reader::forwarding` to `yes` in the sstable
range reader creator method and in the
`mutation_source::make_reader()`.
I couldn't assume that all callers are passing what they mean as the
value for that parameter. I found many sites in tests that create
forwardable single partition readers. This is also something we should
address soon.
Tests: unit(release, debug:v3)
"
* 'sstables-consolidate-reader-factory-methods-v4' of https://github.com/denesb/scylla:
cql_query_test: add unit test covering the non-optimal TWCS sstable read path
sstable_mutation_reader: consolidate constructors
tests: don't pass temporary ranges to readers
sstables: sstable_mutation_reader: remove now unused whole sstable constructor
sstables: stats: remove now unused sstable_partition_reads counter
sstable: remove read_.*row.*_flat() methods
tree-wide: use sstables::make_reader() instead of the read_.*row.*_flat() methods
sstables: pass partition_range to create_single_key_sstable_reader()
sstables: sstable: add make_reader()
"
Currently we have two parallel query paths:
* database::query() -> table::query() -> data_query()
* mutation::query()
The former is used by single partition queries, the latter by range
scans, as mutation::query() is used to convert reconcilable_result to
query::result (which means it is also used in single partition queries
if it triggers read repair). This is a rather unfortunate situation as
we have two parallel implementation of the query code, which means they
are prone to diverge, and in fact they already have -- more on that
later.
This patchset aims to remedy this situation by retiring
`mutation::query()` and migrating users to an implementation based on
the "standard" query path, in other words one using the same building
blocks as the `database::query()` path. This means using
`compact_mutation` for compacting and `query_result_builder` for result
building. These components however were created to work with
`flat_mutation_reader`, however introducing a reader into this pipeline
would mean that we'd have to make all the related APIs asynchronous,
which would cause an insane amount of churn. To avoid this, this
patchset adds an API compatible `consume()` method to `mutation`, which
can accept a `compact_mutation` instance as-is. This allows an elegant
and succinct reimplementation. So far so good.
Like mentioned above, the two implementations have diverged in time, or
have been different from the start. The difference manifest when
calculating digests, more precisely in which tombstones are included in
the digest. The retired `mutation::query()` path incorporates only
non-purgeable tombstones in the digest. The standard query path however
incorporates all tombstones, even those that can be purged. After some
scrutiny however this difference proved to be completely theoretical,
as
the code path where this would matter -- converting reconcilable result
to query result -- passes min timestamp as the query time to the
compaction, so nothing is compacted and hence the difference has no
chance to manifest.
This patch-set was motivated by the desire to provide a single solution
to #7434, instead of two, one for each path.
Tests: unit(release:v2, debug:v2, dev:v3)
"
* 'unified-query-path/v3' of https://github.com/denesb/scylla:
mutation: remove now unused query() and query_compacted()
treewide: use query_mutations() instead of mutation::query()
mutation_test: test_query_digest: ensure digest is produced consistently
mutation_query: introduce query_mutation()
mutation_query: to_data_query_result(): migrate to standard query code
mutation_query: move to_data_query_result() to mutation_partition.cc
mutation: add consume()
flat_mutation_reader: move mutation consumer concepts to separate header
mutation compactor: query compaction: ignore purgeable tombstones
If possible, test the highest sstable format version,
as it's the mostly used.
If there pre-written sstables we need to load from the
test directory from an older version, either specify their
version explicitly, or use the new test_env::reusable_sst
method that looks up the latest sstable version in the
given directory and generation.
Test: unit(release)
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
Message-Id: <20201210161822.2833510-1-bhalevy@scylladb.com>
External updater may do some preparatory work like constructing a new sstable list,
and at the end atomically replace the old list by the new one.
Decoupling the preparation from execution will give us the following benefits:
- the preparation step can now yield if needed to avoid reactor stalls, as it's
been futurized.
- the execution step will now be able to provide strong exception guarantees, as
it's now decoupled from the preparation step which can be non-exception-safe.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
There's a perf_bptree test that compares B+ tree collection with
std::set and std::map ones. There will come more, also the "patterns"
to compare are not just "fill with keys" and "drain to empty", so
here's the perf_collection test, that measures timings of
- fill with keys
- drain key by key
- empty with .clear() call
- full scan with iterator
- insert-and-remove of a single element
for currently used collections
- std::set
- std::map
- intrusive_set_external_comparator
- bplus::tree
* https://github.com/xemul/scylla/tree/br-perf-collection-test:
test: Generalize perf_bptree into perf_collection
perf_collection: Clear collection between itartions
perf_collection: Add intrusive_set_external_comparator
perf_collection: Add test for single element insertion
perf_collection: Add test for destruction with .clear()
perf_collection: Add test for full scan time
After recent sstables manager rework the sstables::test_env must be .close()d
after usage, otherwise the ~sstables_mananger() hits the _closing assertion.
Do it with the help of .do_with(). The execution context is already seastar::async
in this place, so .get() it explicitly.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
In some cases a collection is used to keep several elements,
so it's good to know this timing.
For example, a mutation_partition keeps a set of rows, if used
in cache it can grow large, if used in mutation to apply, it's
typically small. Plain replacement of bst into b-tree caused
performance degardation of mutation application because b-tree
is only better at big sizes.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
This collection is widely used, any replacement should be
compared against it to better understand pros-n-cons.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
We want to start tracking the memory consumption of mutation fragments.
For this we need schema and permit during construction, and on each
modification, so the memory consumption can be recalculated and pass to
the permit.
In this patch we just add the new parameters and go through the insane
churn of updating all call sites. They will be used in the next patch.
We will soon want to update the memory consumption of mutation fragment
after each modification done to it, to do that safely we have to forbid
direct access to the underlying data and instead have callers pass a
lambda doing their modifications.
Uses where this method was just used to move the fragment away are
converted to use `as_clustering_row() &&`.
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`.
C++20 introduced `contains` member functions for maps and sets for
checking whether an element is present in the collection. Previously
`count` function was often used in various ways.
`contains` does not only express the intend of the code better but also
does it in more unified way.
This commit replaces all the occurences of the `count` with the
`contains`.
Tests: unit(dev)
Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>
Message-Id: <b4ef3b4bc24f49abe04a2aba0ddd946009c9fcb2.1597314640.git.piotr@scylladb.com>
"
This series adds support for the "md" sstable format.
Support is based on the following:
* do not use clustering based filtering in the presence
of static row, tombstones.
* Disabling min/max column names in the metadata for
formats older than "md".
* When updating the metadata, reset and disable min/max
in the presence of range tombstones (like Cassandra does
and until we process them accurately).
* Fix the way we maintain min/max column names by:
keeping whole clustering key prefixes as min/max
rather than calculating min/max independently for
each component, like Cassandra does in the "md" format.
Fixes#4442
Tests: unit(dev), cql_query_test -t test_clustering_filtering* (debug)
md migration_test dtest from git@github.com:bhalevy/scylla-dtest.git migration_test-md-v1
"
* tag 'md-format-v4' of github.com:bhalevy/scylla: (27 commits)
config: enable_sstables_md_format by default
test: cql_query_test: add test_clustering_filtering unit tests
table: filter_sstable_for_reader: allow clustering filtering md-format sstables
table: create_single_key_sstable_reader: emit partition_start/end for empty filtered results
table: filter_sstable_for_reader: adjust to md-format
table: filter_sstable_for_reader: include non-scylla sstables with tombstones
table: filter_sstable_for_reader: do not filter if static column is requested
table: filter_sstable_for_reader: refactor clustering filtering conditional expression
features: add MD_SSTABLE_FORMAT cluster feature
config: add enable_sstables_md_format
database: add set_format_by_config
test: sstable_3_x_test: test both mc and md versions
test: Add support for the "md" format
sstables: mx/writer: use version from sstable for write calls
sstables: mx/writer: update_min_max_components for partition tombstone
sstables: metadata_collector: support min_max_components for range tombstones
sstable: validate_min_max_metadata: drop outdated logic
sstables: rename mc folder to mx
sstables: may_contain_rows: always true for old formats
sstables: add may_contain_rows
...
C++20 introduced `contains` member functions for maps and sets for
checking whether an element is present in the collection. Previously
the code pattern looked like:
<collection>.find(<element>) != <collection>.end()
In C++20 the same can be expressed with:
<collection>.contains(<element>)
This is not only more concise but also expresses the intend of the code
more clearly.
This commit replaces all the occurences of the old pattern with the new
approach.
Tests: unit(dev)
Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>
Message-Id: <f001bbc356224f0c38f06ee2a90fb60a6e8e1980.1597132302.git.piotr@scylladb.com>
MD format is disabled by default at this point.
The option extends enable_sstables_mc_format
so that both are needed to be set for supporting
the md format.
The MD_FORMAT cluster feature will be added in
a following patch.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
"
While working on another patch I was getting odd compiler errors
saying that a call to ::make_shared was ambiguous. The reason was that
seastar has both:
template <typename T, typename... A>
shared_ptr<T> make_shared(A&&... a);
template <typename T>
shared_ptr<T> make_shared(T&& a);
The second variant doesn't exist in std::make_shared.
This series drops the dependency in scylla, so that a future change
can make seastar::make_shared a bit more like std::make_shared.
"
* 'espindola/make_shared' of https://github.com/espindola/scylla:
Everywhere: Explicitly instantiate make_lw_shared
Everywhere: Add a make_shared_schema helper
Everywhere: Explicitly instantiate make_shared
cql3: Add a create_multi_column_relation helper
main: Return a shared_ptr from defer_verbose_shutdown
If somebody wants to bypass proper memory accounting they should at
the very least be forced to consider if that is indeed wise and think a
second about the limit they want to apply.
This replaces a lot of make_lw_shared(schema(...)) with
make_shared_schema(...).
This makes it easier to drop a dependency on the differences between
seastar::make_shared and std::make_shared.
Signed-off-by: Rafael Ávila de Espíndola <espindola@scylladb.com>
The row cache memory footprint changed after switch to B+
because we no longer have a sole cache_entry allocation, but
also the bplus::data and bplus::node. Knowing their sizes
helps analyzing the footprint changes.
Also print the size of memtable_entry that's now also stored
in B+'s data.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
The row_cache::partitions_type is replaced from boost::intrusive::set
to bplus::tree<Key = int64_t, T = array_trusted_bounds<cache_entry>>
Where token is used to quickly locate the partition by its token and
the internal array -- to resolve hashing conflicts.
Summary of changes in cache_entry:
- compare's goes away as the new collection needs tri-compare one which
is provided by ring_position_comparator
- when initialized the dummy entry is added with "after_all_keys" kind,
not "before_all_keys" as it was by default. This is to make tree
entries sorted by token
- insertion and removing of cache_entries happens inside double_decker,
most of the changes in row_cache.cc are about passing constructor args
from current_allocator.construct into double_decker.empace_before()
- the _flags is extended to keep array head/tail bits. There's a room
for it, sizeof(cache_entry) remains unchanged
The rest fits smothly into the double_decker API.
Also, as was told in the previous patch, insertion and removal _may_
invalidate iterators, but may leave them intact. However, currently
this doesn't seem to be a problem as the cache_tracker ::insert() and
::on_partition_erase do invalidate iterators unconditionally.
Later this can be otimized, as iterators are invalidated by double-decker
only in case of hash conflict, otherwise it doesn't change arrays and
B+ tree doesn't invalidate its.
tests: unit(dev), perf(dev)
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
// The story is at
// https://groups.google.com/forum/#!msg/scylladb-dev/sxqTHM9rSDQ/WqwF1AQDAQAJ
This is the B+ version which satisfies several specific requirements
to be suitable for row-cache usage.
1. Insert/Remove doesn't invalidate iterators
2. Elements should be LSA-compactable
3. Low overhead of data nodes (1 pointer)
4. External less-only comparator
5. As little actions on insert/delete as possible
6. Iterator walks the sorted keys
The design, briefly is:
There are 3 types of nodes: inner, leaf and data, inner and leaf
keep build-in array of N keys and N(+1) nodes. Leaf nodes sit in
a doubly linked list. Data nodes live separately from the leaf ones
and keep pointers on them. Tree handler keeps pointers on root and
left-most and right-most leaves. Nodes do _not_ keep pointers or
references on the tree (except 3 of them, see below).
changes in v9:
- explicitly marked keys/kids indices with type aliases
- marked the whole erase/clear stuff noexcept
- disposers now accept object pointer instead of reference
- clear tree in destructor
- added more comments
- style/readability review comments fixed
Prior changes
**
- Add noexcepts where possible
- Restrict Less-comparator constraint -- it must be noexcept
- Generalized node_id
- Packed code for beging()/cbegin()
**
- Unsigned indices everywhere
- Cosmetics changes
**
- Const iterators
- C++20 concepts
**
- The index_for() implmenetation is templatized the other way
to make it possible for AVX key search specialization (further
patching)
**
- Insertion tries to push kids to siblings before split
Before this change insertion into full node resulted into this
node being split into two equal parts. This behaviour for random
keys stress gives a tree with ~2/3 of nodes half-filled.
With this change before splitting the full node try to push one
element to each of the siblings (if they exist and not full).
This slows the insertion a bit (but it's still way faster than
the std::set), but gives 15% less total number of nodes.
- Iterator method to reconstruct the data at the given position
The helper creates a new data node, emplaces data into it and
replaces the iterator's one with it. Needed to keep arrays of
data in tree.
- Milli-optimize erase()
- Return back an iterator that will likely be not re-validated
- Do not try to update ancestors separation key for leftmost kid
This caused the clear()-like workload work poorly as compared to
std:set. In particular the row_cache::invalidate() method does
exactly this and this change improves its timing.
- Perf test to measure drain speed
- Helper call to collect tree counters
**
- Fix corner case of iterator.emplace_before()
- Clean heterogenous lookup API
- Handle exceptions from nodes allocations
- Explicitly mark places where the key is copied (for future)
- Extend the tree.lower_bound() API to report back whether
the bound hit the key or not
- Addressed style/cleanness review comments
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
