Fixes some typos as found by codespell run on the code.
In this commit, I was hoping to fix only comments, not user-visible alerts, output, etc.
Follow-up commits will take care of them.
Refs: https://github.com/scylladb/scylladb/issues/16255
Signed-off-by: Yaniv Kaul <yaniv.kaul@scylladb.com>
in C++20, compiler generate operator!=() if the corresponding
operator==() is already defined, the language now understands
that the comparison is symmetric in the new standard.
fortunately, our operator!=() is always equivalent to
`! operator==()`, this matches the behavior of the default
generated operator!=(). so, in this change, all `operator!=`
are removed.
in addition to the defaulted operator!=, C++20 also brings to us
the defaulted operator==() -- it is able to generated the
operator==() if the member-wise lexicographical comparison.
under some circumstances, this is exactly what we need. so,
in this change, if the operator==() is also implemented as
a lexicographical comparison of all memeber variables of the
class/struct in question, it is implemented using the default
generated one by removing its body and mark the function as
`default`. moreover, if the class happen to have other comparison
operators which are implemented using lexicographical comparison,
the default generated `operator<=>` is used in place of
the defaulted `operator==`.
sometimes, we fail to mark the operator== with the `const`
specifier, in this change, to fulfil the need of C++ standard,
and to be more correct, the `const` specifier is added.
also, to generate the defaulted operator==, the operand should
be `const class_name&`, but it is not always the case, in the
class of `version`, we use `version` as the parameter type, to
fulfill the need of the C++ standard, the parameter type is
changed to `const version&` instead. this does not change
the semantic of the comparison operator. and is a more idiomatic
way to pass non-trivial struct as function parameters.
please note, because in C++20, both operator= and operator<=> are
symmetric, some of the operators in `multiprecision` are removed.
they are the symmetric form of the another variant. if they were
not removed, compiler would, for instance, find ambiguous
overloaded operator '=='.
this change is a cleanup to modernize the code base with C++20
features.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#13687
Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
There are two tricky places about corner leaves pointers
managements. Add comments describing the magic.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
When failed-to-be-cloned node cleans itself it must also clear
all its child nodes. Plain destroy() doesn't do it, it only
frees the provided node.
fixes: #9248
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
The node in this place is not yet attached to its parent, so
in btree::debug::yes (tests only) mode the node::drop()'s parent
checks will access null parent pointer.
However, in non-tesing runtime there's a chance that a linear
node fails to clone one of its keys and gets here. In this case
it will carry both leftmost and rightmost flags and the assertion
in drop will fire.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Get rid of unused includes of seastar/util/{defer,closeable}.hh
and add a few that are missing from source files.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
The non-const iterator has constructor from key pointer and
the tree_if_singular method. There's no reasons why these
two are absent in the const_iterator.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
The const_iterator cannot modify anything, but the plain
iterator has public methods to remove the key from the tree.
To control how the tree is modified this method must be
marked private and modification by iterator should come
from somewhere else.
This somewhere else is the existing key_grabber that's
already used to move keys between trees. Generalize this
ability to move a key out of a tree (i.e. -- erase).
Once done -- mark the iterator::erase_and_dispose private.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
The helper is used to walk the tree key-by-key destroying it
in the mean time. Current implementation of this method just
uses the "regular" erasing code which actually rebalances the
tree despite the name.
The biggest problem with removing the rebalancing is that at
some point non-balanced tree may have the left-most key on an
inner node, so to make 100% rebalance-less unlink every other
method of the tree would have to be prepared for that. However,
there's an option to make "light rebalance" (as it's called in
this patch) that only maintains this crucial property of the
tree -- the left-most key is on the leaf.
Some more tech details. Current rebalancer starts when the
node population falls below 1/2 of its capacity and tries to
- grab a key from one of the siblings if it's balanced
- merge two siblings together if they are small enough
The light rebalance is lighter in two ways. First, it leaves
the node unbalanced until it becomes empty. And then it goes
ahead and replaces it with the next sibling.
This change removes ~60% of the keys movements on random test.
Keys still move when the sibling replace happens because in
this case the separation key needs to be placed at the right
sibling 0 position which means shifting all its keys right.
tests: unit(debug)
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Message-Id: <20210623083836.27491-1-xemul@scylladb.com>
Usually lsa allocation is performed with the construct() helper that
allocates a sizeof(T) slot and constructs it in place. Some rare
objects have dynamic size, so they are created by alloc()ating a
slot of some specific size and (!) must provide the correct overload
of size_for_allocation_strategy that reports back the relevant
storage size.
This "must provide" is not enforced, if missed a default sizer would
be instantiated, but won't work properly. This patch makes all users
of alloc() conform to DynamicObject concept which requires the
presense of .storage_size() method to tell that size.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Todays alloc() accepts migrate-fn, size and alignment. All the callers
don't really need to provide anything special for the migrate-fn and
are just happy with default alignof() for alignment. The simplification
is in providing alloc() that only accepts size arg and does the rest
itself.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
The btree's iterators allow for simple checking for '== tree.end()'
condition. For this check neither the tree itself, nor the ending
iterator is required. One just need to check if the _idx value is
the npos.
One additional change to make it work is required -- when removing
an entry from the inline node the _idx should be set to npos.
This change is, well, a bugfix. An iterator left with 0 in _idx is
treated as a valid one. However, the bug is non-triggerable. If such
an "invalid" iterator is compared against tree.end() the check would
return true, because the tree pointers would conside.
So this patch adds an operator bool() to btree iterator to facilitate
simpler checking if it reached the end of the collection or not.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
It turned out that all the users of btree can already be converted
to use safer std::strong_ordering. The only meaningful change here
is the btree code itself -- no more ints there.
tests: unit(dev)
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Message-Id: <20210330153648.27049-1-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>
