[PATCH v2 0/4] box: introduce hint option for memtx tree index

[Kirill Shcherbatov <kshcherbatov@tarantool.org>]

Reworked memtx tree to use 'tuple hints'.
Introduced special functions for retrieve tuple hints for a particular key_def.
Hint is an integer that can be used for tuple comparison optimization:
if a hint of one tuple is less than a hint of another then the first
tuple is definitely less than the second; only if hints are equal
tuple_compare must be called for getting comparison result.

Hints are only useful when:

* they are precalculated and stored along with the tuple;
  calculation is not cheap (cheaper than tuple_compare btw) but
  precalculated hints allow to compare tuples without even fetching
  tuple data.
* first part of key_def is 'string', 'unsigned' or 'integer'
* since hint is calculated using only the first part of key_def
  (and only first several characters if it is a string) this part
  must be different with high probability for every tuple pair.

Enabled hint option improve performance on average by 15%; Select operations
are significantly accelerated (there are scenarios in which the difference
reaches 200-250%).

Changes in version 2:
  -- Splitted patch to parts in other way to decrease diff
  -- Hints are not index option anymore, but default where possible
  -- Removed hints for numeric types

http://github.com/tarantool/tarantool/tree/kshch/gh-3961-tuple-hints
https://github.com/tarantool/tarantool/issues/3961

Alexandr Lyapunov (1):
  box: introduce tuple compare hint for string index

Kirill Shcherbatov (3):
  box: move memtx_tree implementation to source file
  box: rework memtx_tree to store arbitrary nodes
  box: rename memtx_tree.c to memtx_tree_impl.h

 src/box/CMakeLists.txt                      |   2 +-
 src/box/key_def.c                           |   1 +
 src/box/key_def.h                           |  44 ++
 src/box/memtx_tree.h                        |  68 +--
 src/box/memtx_tree_decl.c                   | 207 +++++++++
 src/box/{memtx_tree.c => memtx_tree_impl.h} | 490 +++++++++++++++-----
 src/box/tuple_compare.cc                    | 101 ++++
 src/box/tuple_compare.h                     |   7 +
 src/coll.c                                  |  45 ++
 src/coll.h                                  |   4 +
 10 files changed, 787 insertions(+), 182 deletions(-)
 create mode 100644 src/box/memtx_tree_decl.c
 rename src/box/{memtx_tree.c => memtx_tree_impl.h} (55%)

-- 
2.20.1