diff options
Diffstat (limited to 'sql/handler.h')
| -rw-r--r-- | sql/handler.h | 14 |
1 files changed, 10 insertions, 4 deletions
diff --git a/sql/handler.h b/sql/handler.h index ea709d9dddc..919e063e1cf 100644 --- a/sql/handler.h +++ b/sql/handler.h @@ -163,7 +163,7 @@ #define HA_DO_INDEX_COND_PUSHDOWN 256 /* Supports Index Condition Pushdown */ /* Data is clustered on this key. This means that when you read the key - you also get the row data in the same block. + you also get the row data without any additional disk reads. */ #define HA_CLUSTERED_INDEX 512 @@ -2314,8 +2314,8 @@ public: /* - Check if the primary key (if there is one) is a clustered key covering - all fields. This means: + Check if the primary key (if there is one) is a clustered and a + reference key. This means: - Data is stored together with the primary key (no secondary lookup needed to find the row data). The optimizer uses this to find out @@ -2326,7 +2326,13 @@ public: - When doing a HA_KEYREAD_ONLY we get also all the primary key parts into the row. This is critical property used by index_merge. - For a clustered primary key, index_flags() returns also HA_CLUSTERED_INDEX + All the above is usually true for engines that store the row + data in the primary key index (e.g. in a b-tree), and use the primary + key value as a position(). InnoDB is an example of such an engine. + + For such a clustered primary key, the following should also hold: + index_flags() should contain HA_CLUSTERED_INDEX + table_flags() should contain HA_TABLE_SCAN_ON_INDEX @retval TRUE yes @retval FALSE No. |