diff options
Diffstat (limited to 'sql/handler.h')
| -rw-r--r-- | sql/handler.h | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/sql/handler.h b/sql/handler.h index 36cb81017c6..12413d6238a 100644 --- a/sql/handler.h +++ b/sql/handler.h @@ -1358,6 +1358,22 @@ void get_sweep_read_cost(TABLE *table, ha_rows nrows, bool interrupted, */ #define HA_MRR_MATERIALIZED_KEYS 256 +/* + The following bits are reserved for use by MRR implementation. The intended + use scenario: + + * sql layer calls handler->multi_range_read_info[_const]() + - MRR implementation figures out what kind of scan it will perform, saves + the result in *mrr_mode parameter. + * sql layer remembers what was returned in *mrr_mode + + * the optimizer picks the query plan (which may or may not include the MRR + scan that was estimated by the multi_range_read_info[_const] call) + + * if the query is an EXPLAIN statement, sql layer will call + handler->multi_range_read_explain_info(mrr_mode) to get a text description + of the picked MRR scan; the description will be a part of EXPLAIN output. +*/ #define HA_MRR_IMPLEMENTATION_FLAG1 512 #define HA_MRR_IMPLEMENTATION_FLAG2 1024 #define HA_MRR_IMPLEMENTATION_FLAG3 2048 |