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Overview
| Comment: | Minor performance improvement and size reduction for the btree-page space allocator. |
|---|---|
| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | descendants | both | trunk |
| Files: | files | file ages | folders |
| SHA1: |
73637d12e31f5489efe37d8cf4ab50a1 |
| User & Date: | drh 2014-08-20 00:54:46 |
Context
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2014-08-20
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| 10:42 | Fix a typo in the showdb usage message. (check-in: 6c66beae user: dan tags: trunk) | |
| 00:54 | Minor performance improvement and size reduction for the btree-page space allocator. (check-in: 73637d12 user: drh tags: trunk) | |
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2014-08-19
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| 23:04 | Modify the memsubsys1-3.1.4 test so that it does not fail arbitrarily due to variations in the behavior of system malloc(). (check-in: d280157d user: drh tags: trunk) | |
Changes
Changes to src/btree.c.
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** the first two bytes past the cell pointer area since presumably this
** allocation is being made in order to insert a new cell, so we will
** also end up needing a new cell pointer.
*/
static int allocateSpace(MemPage *pPage, int nByte, int *pIdx){
const int hdr = pPage->hdrOffset; /* Local cache of pPage->hdrOffset */
u8 * const data = pPage->aData; /* Local cache of pPage->aData */
int nFrag; /* Number of fragmented bytes on pPage */
int top; /* First byte of cell content area */
int gap; /* First byte of gap between cell pointers and cell content */
int rc; /* Integer return code */
int usableSize; /* Usable size of the page */
assert( sqlite3PagerIswriteable(pPage->pDbPage) );
assert( pPage->pBt );
................................................................................
assert( sqlite3_mutex_held(pPage->pBt->mutex) );
assert( nByte>=0 ); /* Minimum cell size is 4 */
assert( pPage->nFree>=nByte );
assert( pPage->nOverflow==0 );
usableSize = pPage->pBt->usableSize;
assert( nByte < usableSize-8 );
nFrag = data[hdr+7];
assert( pPage->cellOffset == hdr + 12 - 4*pPage->leaf );
gap = pPage->cellOffset + 2*pPage->nCell;
top = get2byteNotZero(&data[hdr+5]);
if( gap>top ) return SQLITE_CORRUPT_BKPT;
testcase( gap+2==top );
testcase( gap+1==top );
testcase( gap==top );
if( nFrag>=60 ){
/* Always defragment highly fragmented pages */
rc = defragmentPage(pPage);
if( rc ) return rc;
top = get2byteNotZero(&data[hdr+5]);
}else if( gap+2<=top ){
/* Search the freelist looking for a free slot big enough to satisfy
** the request. The allocation is made from the first free slot in
................................................................................
int x = size - nByte;
testcase( x==4 );
testcase( x==3 );
if( x<4 ){
/* Remove the slot from the free-list. Update the number of
** fragmented bytes within the page. */
memcpy(&data[addr], &data[pc], 2);
data[hdr+7] = (u8)(nFrag + x);
}else if( size+pc > usableSize ){
return SQLITE_CORRUPT_BKPT;
}else{
/* The slot remains on the free-list. Reduce its size to account
** for the portion used by the new allocation. */
put2byte(&data[pc+2], x);
}
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** the first two bytes past the cell pointer area since presumably this
** allocation is being made in order to insert a new cell, so we will
** also end up needing a new cell pointer.
*/
static int allocateSpace(MemPage *pPage, int nByte, int *pIdx){
const int hdr = pPage->hdrOffset; /* Local cache of pPage->hdrOffset */
u8 * const data = pPage->aData; /* Local cache of pPage->aData */
int top; /* First byte of cell content area */
int gap; /* First byte of gap between cell pointers and cell content */
int rc; /* Integer return code */
int usableSize; /* Usable size of the page */
assert( sqlite3PagerIswriteable(pPage->pDbPage) );
assert( pPage->pBt );
................................................................................
assert( sqlite3_mutex_held(pPage->pBt->mutex) );
assert( nByte>=0 ); /* Minimum cell size is 4 */
assert( pPage->nFree>=nByte );
assert( pPage->nOverflow==0 );
usableSize = pPage->pBt->usableSize;
assert( nByte < usableSize-8 );
assert( pPage->cellOffset == hdr + 12 - 4*pPage->leaf );
gap = pPage->cellOffset + 2*pPage->nCell;
assert( gap<=65536 );
top = get2byte(&data[hdr+5]);
if( gap>top ){
if( top==0 ){
top = 65536;
}else{
return SQLITE_CORRUPT_BKPT;
}
}
testcase( gap+2==top );
testcase( gap+1==top );
testcase( gap==top );
if( data[hdr+7]>=60 ){
/* Always defragment highly fragmented pages */
rc = defragmentPage(pPage);
if( rc ) return rc;
top = get2byteNotZero(&data[hdr+5]);
}else if( gap+2<=top ){
/* Search the freelist looking for a free slot big enough to satisfy
** the request. The allocation is made from the first free slot in
................................................................................
int x = size - nByte;
testcase( x==4 );
testcase( x==3 );
if( x<4 ){
/* Remove the slot from the free-list. Update the number of
** fragmented bytes within the page. */
memcpy(&data[addr], &data[pc], 2);
data[hdr+7] += (u8)x;
}else if( size+pc > usableSize ){
return SQLITE_CORRUPT_BKPT;
}else{
/* The slot remains on the free-list. Reduce its size to account
** for the portion used by the new allocation. */
put2byte(&data[pc+2], x);
}
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