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Change the internal btree routine moveToRoot() to return SQLITE_EMPTY if

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the table is empty or if it has pgnoRoot==0.  This simplifies the callers,
making them smaller and faster.  The SQLITE_EMPTY result code is intercepted
and changed into SQLITE_OK before surfacing in an API.

FossilOrigin-Name: 240d57143d943eaddd5f7c2d473f47a1d29417e61d28142f70f3d960bb9b30df
This commit is contained in:
drh
2017-08-14 18:13:52 +00:00
parent f0357d8b2c
commit 44548e7218
4 changed files with 44 additions and 43 deletions
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69
src/btree.c
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@@ -4914,9 +4914,9 @@ static void moveToParent(BtCursor *pCur){
** single child page. This can only happen with the table rooted at page 1.
**
** If the b-tree structure is empty, the cursor state is set to
** CURSOR_INVALID. Otherwise, the cursor is set to point to the first
** cell located on the root (or virtual root) page and the cursor state
** is set to CURSOR_VALID.
** CURSOR_INVALID and this routine returns SQLITE_EMPTY. Otherwise,
** the cursor is set to point to the first cell located on the root
** (or virtual root) page and the cursor state is set to CURSOR_VALID.
**
** If this function returns successfully, it may be assumed that the
** page-header flags indicate that the [virtual] root-page is the expected
@@ -4935,6 +4935,7 @@ static int moveToRoot(BtCursor *pCur){
assert( CURSOR_VALID < CURSOR_REQUIRESEEK );
assert( CURSOR_FAULT > CURSOR_REQUIRESEEK );
assert( pCur->eState < CURSOR_REQUIRESEEK || pCur->iPage<0 );
assert( pCur->pgnoRoot>0 || pCur->iPage<0 );
if( pCur->iPage>=0 ){
if( pCur->iPage ){
@@ -4946,7 +4947,7 @@ static int moveToRoot(BtCursor *pCur){
}
}else if( pCur->pgnoRoot==0 ){
pCur->eState = CURSOR_INVALID;
return SQLITE_OK;
return SQLITE_EMPTY;
}else{
assert( pCur->iPage==(-1) );
if( pCur->eState>=CURSOR_REQUIRESEEK ){
@@ -4999,6 +5000,7 @@ skip_init:
rc = moveToChild(pCur, subpage);
}else{
pCur->eState = CURSOR_INVALID;
rc = SQLITE_EMPTY;
}
return rc;
}
@@ -5065,14 +5067,13 @@ int sqlite3BtreeFirst(BtCursor *pCur, int *pRes){
assert( sqlite3_mutex_held(pCur->pBtree->db->mutex) );
rc = moveToRoot(pCur);
if( rc==SQLITE_OK ){
if( pCur->eState==CURSOR_INVALID ){
assert( pCur->pgnoRoot==0 || pCur->apPage[pCur->iPage]->nCell==0 );
*pRes = 1;
}else{
assert( pCur->apPage[pCur->iPage]->nCell>0 );
*pRes = 0;
rc = moveToLeftmost(pCur);
}
assert( pCur->apPage[pCur->iPage]->nCell>0 );
*pRes = 0;
rc = moveToLeftmost(pCur);
}else if( rc==SQLITE_EMPTY ){
assert( pCur->pgnoRoot==0 || pCur->apPage[pCur->iPage]->nCell==0 );
*pRes = 1;
rc = SQLITE_OK;
}
return rc;
}
@@ -5104,20 +5105,18 @@ int sqlite3BtreeLast(BtCursor *pCur, int *pRes){
rc = moveToRoot(pCur);
if( rc==SQLITE_OK ){
if( CURSOR_INVALID==pCur->eState ){
assert( pCur->pgnoRoot==0 || pCur->apPage[pCur->iPage]->nCell==0 );
*pRes = 1;
assert( pCur->eState==CURSOR_VALID );
*pRes = 0;
rc = moveToRightmost(pCur);
if( rc==SQLITE_OK ){
pCur->curFlags |= BTCF_AtLast;
}else{
assert( pCur->eState==CURSOR_VALID );
*pRes = 0;
rc = moveToRightmost(pCur);
if( rc==SQLITE_OK ){
pCur->curFlags |= BTCF_AtLast;
}else{
pCur->curFlags &= ~BTCF_AtLast;
}
pCur->curFlags &= ~BTCF_AtLast;
}
}else if( rc==SQLITE_EMPTY ){
assert( pCur->pgnoRoot==0 || pCur->apPage[pCur->iPage]->nCell==0 );
*pRes = 1;
rc = SQLITE_OK;
}
return rc;
}
@@ -5216,16 +5215,17 @@ int sqlite3BtreeMovetoUnpacked(
rc = moveToRoot(pCur);
if( rc ){
if( rc==SQLITE_EMPTY ){
assert( pCur->pgnoRoot==0 || pCur->apPage[pCur->iPage]->nCell==0 );
*pRes = -1;
return SQLITE_OK;
}
return rc;
}
assert( pCur->pgnoRoot==0 || pCur->apPage[pCur->iPage] );
assert( pCur->pgnoRoot==0 || pCur->apPage[pCur->iPage]->isInit );
assert( pCur->eState==CURSOR_INVALID || pCur->apPage[pCur->iPage]->nCell>0 );
if( pCur->eState==CURSOR_INVALID ){
*pRes = -1;
assert( pCur->pgnoRoot==0 || pCur->apPage[pCur->iPage]->nCell==0 );
return SQLITE_OK;
}
assert( pCur->apPage[pCur->iPage] );
assert( pCur->apPage[pCur->iPage]->isInit );
assert( pCur->eState==CURSOR_VALID );
assert( pCur->apPage[pCur->iPage]->nCell > 0 );
assert( pCur->apPage[0]->intKey==pCur->curIntKey );
assert( pCur->curIntKey || pIdxKey );
for(;;){
@@ -8439,6 +8439,7 @@ int sqlite3BtreeDelete(BtCursor *pCur, u8 flags){
btreeReleaseAllCursorPages(pCur);
pCur->eState = CURSOR_REQUIRESEEK;
}
if( rc==SQLITE_EMPTY ) rc = SQLITE_OK;
}
}
return rc;
@@ -8903,11 +8904,11 @@ int sqlite3BtreeCount(BtCursor *pCur, i64 *pnEntry){
i64 nEntry = 0; /* Value to return in *pnEntry */
int rc; /* Return code */
if( pCur->pgnoRoot==0 ){
rc = moveToRoot(pCur);
if( rc==SQLITE_EMPTY ){
*pnEntry = 0;
return SQLITE_OK;
}
rc = moveToRoot(pCur);
/* Unless an error occurs, the following loop runs one iteration for each
** page in the B-Tree structure (not including overflow pages).