Re: [PATCH v1 4/4] box: introduce hint option for memtx tree index

[Vladimir Davydov <vdavydov.dev@gmail.com>]

On Tue, Feb 05, 2019 at 02:58:39PM +0300, Kirill Shcherbatov wrote:
> If an index has certain option, a compare hint must be calculated
> and stored within bps_tree along with struct tuple pointer. This
> hint must be used for tuple precomparison in order to avoid memory
> fetching and significantly improve tree performance.
> 
> Such a hinted tree will cost twice amount of memory - 20 byte per
> tuple on average.
> Enabled hint option improve performance on average by 15%; Select
> operations are significantly accelerated (there are scenarios in
> which the difference reaches 200-250%).
> 
> Test set from original @alyapunov patch.
> 
> Needed for #3961
> ---
>  src/box/index_def.c                 |   2 +
>  src/box/index_def.h                 |   6 +
>  src/box/lua/schema.lua              |  12 ++
>  src/box/lua/space.cc                |   5 +
>  src/box/memtx_tree.c                | 192 +++++++++++++++++++++++-
>  src/box/memtx_tree_impl.h           |   2 +-
>  test/box/tree_pk.result             | 220 ++++++++++++++++++++++++++++
>  test/box/tree_pk.test.lua           |  88 +++++++++++
>  test/box/tree_pk_multipart.result   | 155 ++++++++++++++++++++
>  test/box/tree_pk_multipart.test.lua |  65 ++++++++
>  10 files changed, 745 insertions(+), 2 deletions(-)
> 
> diff --git a/src/box/index_def.c b/src/box/index_def.c
> index c52aa38d1..4d3fadc6e 100644
> --- a/src/box/index_def.c
> +++ b/src/box/index_def.c
> @@ -49,6 +49,7 @@ const struct index_opts index_opts_default = {
>  	/* .bloom_fpr           = */ 0.05,
>  	/* .lsn                 = */ 0,
>  	/* .stat                = */ NULL,
> +	/* .hint                = */ false,
>  };
>  
>  const struct opt_def index_opts_reg[] = {
> @@ -62,6 +63,7 @@ const struct opt_def index_opts_reg[] = {
>  	OPT_DEF("run_size_ratio", OPT_FLOAT, struct index_opts, run_size_ratio),
>  	OPT_DEF("bloom_fpr", OPT_FLOAT, struct index_opts, bloom_fpr),
>  	OPT_DEF("lsn", OPT_INT64, struct index_opts, lsn),
> +	OPT_DEF("hint", OPT_BOOL, struct index_opts, hint),
>  	OPT_END,
>  };
>  
> diff --git a/src/box/index_def.h b/src/box/index_def.h
> index 7717ecd64..74814bef5 100644
> --- a/src/box/index_def.h
> +++ b/src/box/index_def.h
> @@ -157,6 +157,10 @@ struct index_opts {
>  	 * LSN from the time of index creation.
>  	 */
>  	int64_t lsn;
> +	/**
> +	 * Use hint optimization for tree index.
> +	 */
> +	bool hint;

Hints should be enabled unconditionally if possible. Please don't
introduce a new index option.

The tests won't be necessary then, I guess.

> diff --git a/src/box/memtx_tree.c b/src/box/memtx_tree.c
> index 6b22883c2..426a11262 100644
> --- a/src/box/memtx_tree.c
> +++ b/src/box/memtx_tree.c
> @@ -79,8 +79,198 @@ struct memtx_tuple_tree_key_data {
>  
>  /* }}} */
>  
> +/* {{{ Memtx hinted and hint_only tree class. *******************/

Please add a comment somewhere explaining what's the difference.

I also have some concerns about struct/function names, but we'll talk
about them later, when you make patch 2 review-able.

> +
> +/**
> + * Struct that is used as a key in BPS tree definition in
> + * metmx_hint_only_tree and metmx_hinted_tree.
> +*/
> +struct memtx_hinted_tree_key_data {
> +	/** Sequence of msgpacked search fields. */
> +	const char *key;
> +	/** Number of msgpacked search fields. */
> +	uint32_t part_count;
> +	/**
> +	 * Compare hint. Is calculated automatically on 'set'
> +	 * operation with memtx_hinted_tree_key_data_set().
> +	 */
> +	uint64_t hint;
> +};