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Improved comments on the FORDELETE hint. No logic changes.

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FossilOrigin-Name: a3cec529f0238e4ca1196fec420f2de80d28db78
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drh
2016-01-21 15:55:37 +00:00
parent b5a5a23e92
commit 9c0c57a4ca
5 changed files with 29 additions and 20 deletions
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16
src/btree.h
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@@ -199,14 +199,24 @@ int sqlite3BtreeNewDb(Btree *p);
** Flags passed as the third argument to sqlite3BtreeCursor().
**
** For read-only cursors the wrFlag argument is always zero. For read-write
** cursors it may be set to either (BTREE_WRCSR|BTREE_FORDELETE) or
** (BTREE_WRCSR). If the BTREE_FORDELETE flag is set, then the cursor will
** cursors it may be set to either (BTREE_WRCSR|BTREE_FORDELETE) or just
** (BTREE_WRCSR). If the BTREE_FORDELETE bit is set, then the cursor will
** only be used by SQLite for the following:
**
** * to seek to and delete specific entries, and/or
** * to seek to and then delete specific entries, and/or
**
** * to read values that will be used to create keys that other
** BTREE_FORDELETE cursors will seek to and delete.
**
** The BTREE_FORDELETE flag is an optimization hint. It is not used by
** by this, the native b-tree engine of SQLite, but it is available to
** alternative storage engines that might be substituted in place of this
** b-tree system. For alternative storage engines in which a delete of
** the main table row automatically deletes corresponding index rows,
** the FORDELETE flag hint allows those alternative storage engines to
** skip a lot of work. Namely: FORDELETE cursors may treat all SEEK
** and DELETE operations as no-ops, and any READ operation against a
** FORDELETE cursor may return a null row: 0x01 0x00.
*/
#define BTREE_WRCSR 0x00000004 /* read-write cursor */
#define BTREE_FORDELETE 0x00000008 /* Cursor is for seek/delete only */