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Update comments on the free-page allocator to accurately reflect the

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latest implementation.  Add new asserts to the free-page allocator.

FossilOrigin-Name: 9a135e37b696b8544da8dbddf9d1041b8fa6f1c2
This commit is contained in:
drh
2013-03-02 03:25:55 +00:00
parent 1d59d036de
commit 82e647d7c3
3 changed files with 22 additions and 18 deletions
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26
src/btree.c
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@@ -4875,21 +4875,23 @@ int sqlite3BtreePrevious(BtCursor *pCur, int *pRes){
** an error. *ppPage and *pPgno are undefined in the event of an error.
** Do not invoke sqlite3PagerUnref() on *ppPage if an error is returned.
**
** If the "nearby" parameter is not 0, then a (feeble) effort is made to
** If the "nearby" parameter is not 0, then an effort is made to
** locate a page close to the page number "nearby". This can be used in an
** attempt to keep related pages close to each other in the database file,
** which in turn can make database access faster.
**
** If the "exact" parameter is not 0, and the page-number nearby exists
** anywhere on the free-list, then it is guarenteed to be returned. This
** is only used by auto-vacuum databases when allocating a new table.
** If the eMode parameter is BTALLOC_EXACT and the nearby page exists
** anywhere on the free-list, then it is guaranteed to be returned. If
** eMode is BTALLOC_LT then the page returned will be less than or equal
** to nearby if any such page exists. If eMode is BTALLOC_ANY then there
** are no restrictions on which page is returned.
*/
static int allocateBtreePage(
BtShared *pBt,
MemPage **ppPage,
Pgno *pPgno,
Pgno nearby,
u8 eMode
BtShared *pBt, /* The btree */
MemPage **ppPage, /* Store pointer to the allocated page here */
Pgno *pPgno, /* Store the page number here */
Pgno nearby, /* Search for a page near this one */
u8 eMode /* BTALLOC_EXACT, BTALLOC_LT, or BTALLOC_ANY */
){
MemPage *pPage1;
int rc;
@@ -4900,6 +4902,7 @@ static int allocateBtreePage(
Pgno mxPage; /* Total size of the database file */
assert( sqlite3_mutex_held(pBt->mutex) );
assert( eMode==BTALLOC_ANY || (nearby>0 && pBt->autoVacuum) );
pPage1 = pBt->pPage1;
mxPage = btreePagecount(pBt);
n = get4byte(&pPage1->aData[36]);
@@ -4912,7 +4915,7 @@ static int allocateBtreePage(
Pgno iTrunk;
u8 searchList = 0; /* If the free-list must be searched for 'nearby' */
/* If the 'exact' parameter was true and a query of the pointer-map
/* If eMode==BTALLOC_EXACT and a query of the pointer-map
** shows that the page 'nearby' is somewhere on the free-list, then
** the entire-list will be searched for that page.
*/
@@ -4942,7 +4945,8 @@ static int allocateBtreePage(
/* The code within this loop is run only once if the 'searchList' variable
** is not true. Otherwise, it runs once for each trunk-page on the
** free-list until the page 'nearby' is located.
** free-list until the page 'nearby' is located (eMode==BTALLOC_EXACT)
** or until a page less than 'nearby' is located (eMode==BTALLOC_LT)
*/
do {
pPrevTrunk = pTrunk;