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ircd::db: Optimize away one of the row ctor's vector heap allocations.

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This commit is contained in:
Jason Volk 2018-11-05 16:37:58 -08:00
parent e03d36aa48
commit cbbfbcac72
1 changed files with 16 additions and 10 deletions
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26
ircd/db.cc
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@ -7720,19 +7720,25 @@ ircd::db::row::row(database &d,
return &d[name];
});
//TODO: allocator
std::vector<ColumnFamilyHandle *> handles(column_count);
std::transform(colptr, colptr + column_count, begin(handles), []
(database::column *const &ptr)
{
return ptr->handle.get();
});
//TODO: does this block?
std::vector<Iterator *> iterators;
{
const ctx::uninterruptible ui;
// The goal here is to optimize away the heap allocation incurred by
// having to pass RocksDB the specific std::vector type which doesn't
// have room for an allocator. We use a single thread_local vector
// and reserve() it with one worst-case size of all possible columns.
// Then we resize it to this specific call's requirements and copy the
// column pointers. On sane platforms only one allocation ever occurs.
const ctx::critical_assertion ca;
thread_local std::vector<ColumnFamilyHandle *> handles;
assert(column_count <= d.columns.size());
handles.reserve(d.columns.size());
handles.resize(column_count);
std::transform(colptr, colptr + column_count, begin(handles), []
(database::column *const &ptr)
{
return ptr->handle.get();
});
throw_on_error
{
d.d->NewIterators(options, handles, &iterators)