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Add the BTREE_FORDELETE and BTREE_AUXDELETE flags to the b-tree layer interface

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and use them.  Add assert() statement to verify that they are correct.

FossilOrigin-Name: 85c467041c9378cae3038756da815e9117ee8c7d
This commit is contained in:
drh
2016-01-30 13:32:30 +00:00
parent 5f4a686f8c df31221d33
commit 4b09ec6e11
10 changed files with 210 additions and 62 deletions
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44
src/btree.c
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@@ -4049,13 +4049,13 @@ int sqlite3BtreeSavepoint(Btree *p, int op, int iSavepoint){
** on the database already. If a write-cursor is requested, then
** the caller is assumed to have an open write transaction.
**
** If wrFlag==0, then the cursor can only be used for reading.
** If wrFlag==1, then the cursor can be used for reading or for
** writing if other conditions for writing are also met. These
** are the conditions that must be met in order for writing to
** be allowed:
** If the BTREE_WRCSR bit of wrFlag is clear, then the cursor can only
** be used for reading. If the BTREE_WRCSR bit is set, then the cursor
** can be used for reading or for writing if other conditions for writing
** are also met. These are the conditions that must be met in order
** for writing to be allowed:
**
** 1: The cursor must have been opened with wrFlag==1
** 1: The cursor must have been opened with wrFlag containing BTREE_WRCSR
**
** 2: Other database connections that share the same pager cache
** but which are not in the READ_UNCOMMITTED state may not have
@@ -4067,6 +4067,16 @@ int sqlite3BtreeSavepoint(Btree *p, int op, int iSavepoint){
**
** 4: There must be an active transaction.
**
** The BTREE_FORDELETE bit of wrFlag may optionally be set if BTREE_WRCSR
** is set. If FORDELETE is set, that is a hint to the implementation that
** this cursor will only be used to seek to and delete entries of an index
** as part of a larger DELETE statement. The FORDELETE hint is not used by
** this implementation. But in a hypothetical alternative storage engine
** in which index entries are automatically deleted when corresponding table
** rows are deleted, the FORDELETE flag is a hint that all SEEK and DELETE
** operations on this cursor can be no-ops and all READ operations can
** return a null row (2-bytes: 0x01 0x00).
**
** No checking is done to make sure that page iTable really is the
** root page of a b-tree. If it is not, then the cursor acquired
** will not work correctly.
@@ -8082,13 +8092,21 @@ end_insert:
/*
** Delete the entry that the cursor is pointing to.
**
** If the second parameter is zero, then the cursor is left pointing at an
** arbitrary location after the delete. If it is non-zero, then the cursor
** is left in a state such that the next call to BtreeNext() or BtreePrev()
** moves it to the same row as it would if the call to BtreeDelete() had
** been omitted.
** If the BTREE_SAVEPOSITION bit of the flags parameter is zero, then
** the cursor is left pointing at an arbitrary location after the delete.
** But if that bit is set, then the cursor is left in a state such that
** the next call to BtreeNext() or BtreePrev() moves it to the same row
** as it would have been on if the call to BtreeDelete() had been omitted.
**
** The BTREE_AUXDELETE bit of flags indicates that is one of several deletes
** associated with a single table entry and its indexes. Only one of those
** deletes is considered the "primary" delete. The primary delete occurs
** on a cursor that is not a BTREE_FORDELETE cursor. All but one delete
** operation on non-FORDELETE cursors is tagged with the AUXDELETE flag.
** The BTREE_AUXDELETE bit is a hint that is not used by this implementation,
** but which might be used by alternative storage engines.
*/
int sqlite3BtreeDelete(BtCursor *pCur, int bPreserve){
int sqlite3BtreeDelete(BtCursor *pCur, u8 flags){
Btree *p = pCur->pBtree;
BtShared *pBt = p->pBt;
int rc; /* Return code */
@@ -8098,6 +8116,7 @@ int sqlite3BtreeDelete(BtCursor *pCur, int bPreserve){
int iCellDepth; /* Depth of node containing pCell */
u16 szCell; /* Size of the cell being deleted */
int bSkipnext = 0; /* Leaf cursor in SKIPNEXT state */
u8 bPreserve = flags & BTREE_SAVEPOSITION; /* Keep cursor valid */
assert( cursorOwnsBtShared(pCur) );
assert( pBt->inTransaction==TRANS_WRITE );
@@ -8107,6 +8126,7 @@ int sqlite3BtreeDelete(BtCursor *pCur, int bPreserve){
assert( !hasReadConflicts(p, pCur->pgnoRoot) );
assert( pCur->aiIdx[pCur->iPage]<pCur->apPage[pCur->iPage]->nCell );
assert( pCur->eState==CURSOR_VALID );
assert( (flags & ~(BTREE_SAVEPOSITION | BTREE_AUXDELETE))==0 );
iCellDepth = pCur->iPage;
iCellIdx = pCur->aiIdx[iCellDepth];