It's shorter, and is supposed to be optimized for trivially-moveable
types.
Important for managed_vector<index_entry>, which can have lots of
elements.
`chunked_managed_vector` is a vector-like container which splits
its contents into multiple contiguous allocations if necessary,
in order to fit within LSA's max preferred contiguous allocation
limits.
Each limited-size chunk is stored in a `managed_vector`.
`managed_vector` is unaware of LSA's size limits.
It's up to the user of `managed_vector` to pick a size which
is small enough.
This happens in `chunked_managed_vector::max_chunk_capacity()`.
But the calculation is wrong, because it doesn't account for
the fact that `managed_vector` has to place some metadata
(the backreference pointer) inside the allocation.
In effect, the chunks allocated by `chunked_managed_vector`
are just a tiny bit larger than the limit, and the limit is violated.
Fix this by accounting for the metadata.
Also, before the patch `chunked_managed_vector::max_contiguous_allocation`,
repeats the definition of logalloc::max_managed_object_size.
This is begging for a bug if `logalloc::max_managed_object_size`
changes one day. Adjust it so that `chunked_managed_vector` looks
directly at `logalloc::max_managed_object_size`, as it means to.
vla (variable length array) is an extension in GCC and Clang. and
it is not part of the C++ standard.
so let's avoid using it if possible, for better standard compliant.
it's also more consistent with other places where we calculate the size
of an array of T in the same source file.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#16084
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
As part of this change, the container for partition index pages was
changed from utils::loading_shared_values to intrusive_btree. This is
to avoid reactor stalls which the former induces with a large number
of elements (pages) due to its use of a hashtable under the hood,
which reallocates contiguous storage.
Will be needed by index reader to ensure that destructor doesn't
invoke the allocator so that all is destroyed in the desried
allocation context before the object is destroyed.
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>
This ensures that row::external_memory_usage() is invariant to
insertion order of cells.
It should be so, so that accounting of a clustering_row, merged from
multiple MVCC versions by the partition_snapshot_flat_reader on behalf
of a memtable flush, doesn't give a greater result than what is used
by the memtable region. Overaccounting leads to assertion failure in
~flush_memory_accounter.
Fixes#3625 (hopefully).
Message-Id: <1535982513-19922-1-git-send-email-tgrabiec@scylladb.com>
Every lsa-allocated object is prefixed by a header that contains information
needed to free or migrate it. This includes its size (for freeing) and
an 8-byte migrator (for migrating). Together with some flags, the overhead
is 14 bytes (16 bytes if the default alignment is used).
This patch reduces the header size to 1 byte (8 bytes if the default alignment
is used). It uses the following techniques:
- ULEB128-like encoding (actually more like ULEB64) so a live object's header
can typically be stored using 1 byte
- indirection, so that migrators can be encoded in a small index pointing
to a migrator table, rather than using an 8-byte pointer; this exploits
the fact that only a small number of types are stored in LSA
- moving the responsibility for determining an object's size to its
migrator, rather than storing it in the header; this exploits the fact
that the migrator stores type information, and object size is in fact
information about the type
The patch improves the results of memory_footprint_test as following:
Before:
- in cache: 976
- in memtable: 947
After:
mutation footprint:
- in cache: 880
- in memtable: 858
A reduction of about 10%. Further reductions are possible by reducing the
alignment of lsa objects.
logalloc_test was adjusted to free more objects, since with the lower
footprint, rounding errors (to full segments) are different and caused
false errors to be detected.
Missing: adjustments to scylla-gdb.py; will be done after we agree on the
new descriptor's format.
Renaming the function to external_memory_usage() makes it clear that
sizeof(T) is not included, something that was a source of confusion in
the past.
Signed-off-by: Paweł Dziepak <pdziepak@scylladb.com>
gcc 6 complains that deleting a managed_bytes::external isn't defined
because the size isn't known. I'm not sure it's correct, but there's no
way to tell because flexible arrays aren't standardized.
Fix by using an array of zero size.
Message-Id: <1466715187-4125-1-git-send-email-avi@scylladb.com>
Clang enforces that a union's constexpr CTOR must initialize
one of the members. The spec is seemingly silent as to what
the rule on this is, however, making this non-constexpr results in clang
accepting the constructor.
Signed-off-by: Erich Keane <erich.keane@verizon.net>
Message-Id: <1454604300-1673-1-git-send-email-erich.keane@verizon.net>
The migrator tells lsa how to move an object when it is compacted.
Currently it is a function pointer, which means we must know how to move
the object at compile time. Making it an object allows us to build the
migration function at runtime, making it suitable for runtime-defined types
(such as tuples and user-defined types).
In the future, we may also store the size there for fixed-size types,
reducing lsa overhead.
C++ variable templates would have made this patch smaller, but unfortunately
they are only supported on gcc 5+.
Copying values may throw (std::bad_alloc for example), which will
result in a leak because destructor will not be called when
constructor throws.
May manifest as the following assertion failure:
utils/logalloc.cc:672: virtual logalloc::region_impl::~region_impl(): Assertion `_active->is_empty()' failed.
