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Optimize queries of the form "SELECT count(*) FROM <tbl>" by adding a sqlite3BtreeCount() interface to the btree layer. (CVS 6316)

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FossilOrigin-Name: d4aa6593183224b6868a322511511c0bbf63b598
This commit is contained in:
danielk1977
2009-02-24 10:01:51 +00:00
parent e2d7b24d08
commit a55331620e
9 changed files with 259 additions and 104 deletions
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71
src/btree.c
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@@ -9,7 +9,7 @@
** May you share freely, never taking more than you give.
**
*************************************************************************
** $Id: btree.c,v 1.566 2009/02/18 20:31:18 drh Exp $
** $Id: btree.c,v 1.567 2009/02/24 10:01:52 danielk1977 Exp $
**
** This file implements a external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
@@ -6751,6 +6751,75 @@ int sqlite3BtreeFlags(BtCursor *pCur){
return pPage->aData[pPage->hdrOffset];
}
#ifndef SQLITE_OMIT_BTREECOUNT
/*
** The first argument, pCur, is a cursor opened on some b-tree. Count the
** number of entries in the b-tree and write the result to *pnEntry.
**
** SQLITE_OK is returned if the operation is successfully executed.
** Otherwise, if an error is encountered (i.e. an IO error or database
** corruption) an SQLite error code is returned.
*/
int sqlite3BtreeCount(BtCursor *pCur, i64 *pnEntry){
i64 nEntry = 0; /* Value to return in *pnEntry */
int rc; /* Return code */
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).
*/
while( rc==SQLITE_OK ){
int iIdx; /* Index of child node in parent */
MemPage *pPage; /* Current page of the b-tree */
/* If this is a leaf page or the tree is not an int-key tree, then
** this page contains countable entries. Increment the entry counter
** accordingly.
*/
pPage = pCur->apPage[pCur->iPage];
if( pPage->leaf || !pPage->intKey ){
nEntry += pPage->nCell;
}
/* pPage is a leaf node. This loop navigates the cursor so that it
** points to the first interior cell that it points to the parent of
** the next page in the tree that has not yet been visited. The
** pCur->aiIdx[pCur->iPage] value is set to the index of the parent cell
** of the page, or to the number of cells in the page if the next page
** to visit is the right-child of its parent.
**
** If all pages in the tree have been visited, return SQLITE_OK to the
** caller.
*/
if( pPage->leaf ){
do {
if( pCur->iPage==0 ){
/* All pages of the b-tree have been visited. Return successfully. */
*pnEntry = nEntry;
return SQLITE_OK;
}
sqlite3BtreeMoveToParent(pCur);
}while ( pCur->aiIdx[pCur->iPage]>=pCur->apPage[pCur->iPage]->nCell );
pCur->aiIdx[pCur->iPage]++;
pPage = pCur->apPage[pCur->iPage];
}
/* Descend to the child node of the cell that the cursor currently
** points at. This is the right-child if (iIdx==pPage->nCell).
*/
iIdx = pCur->aiIdx[pCur->iPage];
if( iIdx==pPage->nCell ){
rc = moveToChild(pCur, get4byte(&pPage->aData[pPage->hdrOffset+8]));
}else{
rc = moveToChild(pCur, get4byte(findCell(pPage, iIdx)));
}
}
/* An error has occured. Return an error code. */
return rc;
}
#endif
/*
** Return the pager associated with a BTree. This routine is used for