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**
** In other words, each time we advance to the next sorter element, log2(N)
** key comparison operations are required, where N is the number of segments
** being merged (rounded up to the next power of 2).
*/
struct VdbeSorter {
int nWorking; /* Start a new b-tree after this many pages */
int nAlloc; /* Allocated size of aIter[] and aTree[] */
int nTree; /* Used size of aTree/aIter (power of 2) */
VdbeSorterIter *aIter; /* Array of iterators to merge */
int *aTree; /* Current state of incremental merge */
i64 iWriteOff; /* Current write offset within file pTemp1 */
sqlite3_file *pTemp1; /* PMA file 1 */
i64 *aOffset; /* Array of PMA offsets for file 1 */
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u8 *aKey; /* Pointer to current key */
};
/* Minimum allowable value for the VdbeSorter.nWorking variable */
#define SORTER_MIN_SEGMENT_SIZE 10
/* Maximum number of segments to merge in a single go */
#define SORTER_MAX_MERGE_COUNT 2
#define SORTER_MAX_MERGE_COUNT 16
/*
** Append integer iOff to the VdbeSorter.aOffset[] array of the sorter object
** passed as the second argument. SQLITE_NOMEM is returned if an OOM error
** is encountered, or SQLITE_OK if no error occurs.
**
** TODO: The aOffset[] array may grow indefinitely. Fix this.
*/
static int vdbeSorterAppendOffset(sqlite3 *db, VdbeSorter *p, i64 iOff){
int *aNew; /* New VdbeSorter.aRoot[] array */
p->aOffset = sqlite3DbReallocOrFree(
db, p->aOffset, (p->nOffset+1)*sizeof(i64)
);
if( !p->aOffset ) return SQLITE_NOMEM;
p->aOffset[p->nOffset++] = iOff;
return SQLITE_OK;
}
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** Free any cursor components allocated by sqlite3VdbeSorterXXX routines.
*/
void sqlite3VdbeSorterClose(sqlite3 *db, VdbeCursor *pCsr){
VdbeSorter *pSorter = pCsr->pSorter;
if( pSorter ){
if( pSorter->aIter ){
int i;
for(i=0; i<pSorter->nAlloc; i++){
for(i=0; i<pSorter->nTree; i++){
vdbeSorterIterZero(db, &pSorter->aIter[i]);
}
sqlite3DbFree(db, pSorter->aIter);
sqlite3DbFree(db, pSorter->aTree);
}
if( pSorter->pTemp1 ){
sqlite3OsCloseFree(pSorter->pTemp1);
}
sqlite3DbFree(db, pSorter->aOffset);
sqlite3DbFree(db, pSorter);
pCsr->pSorter = 0;
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rc = sqlite3BtreeCursor(pCsr->pBt, iRoot, 1, pCsr->pKeyInfo, p);
}
}
}
return rc;
}
/*
** Extend the pSorter->aIter[] and pSorter->aTree[] arrays using DbRealloc().
** Return SQLITE_OK if successful, or SQLITE_NOMEM otherwise.
*/
static int vdbeSorterGrowArrays(sqlite3* db, VdbeSorter *pSorter){
int *aTree; /* New aTree[] allocation */
VdbeSorterIter *aIter; /* New aIter[] allocation */
int nOld = pSorter->nAlloc; /* Current size of arrays */
int nNew = (nOld?nOld*2:4); /* Size of arrays after reallocation */
/* Realloc aTree[]. */
aTree = sqlite3DbRealloc(db, pSorter->aTree, sizeof(int)*nNew);
if( !aTree ) return SQLITE_NOMEM;
memset(&aTree[nOld], 0, (nNew-nOld) * sizeof(int));
pSorter->aTree = aTree;
/* Realloc aIter[]. */
aIter = sqlite3DbRealloc(db, pSorter->aIter, sizeof(VdbeSorterIter)*nNew);
if( !aIter ) return SQLITE_NOMEM;
memset(&aIter[nOld], 0, (nNew-nOld) * sizeof(VdbeSorterIter));
pSorter->aIter = aIter;
/* Set VdbeSorter.nAlloc to the new size of the arrays and return OK. */
pSorter->nAlloc = nNew;
return SQLITE_OK;
}
/*
** Helper function for sqlite3VdbeSorterRewind().
*/
static int vdbeSorterInitMerge(
sqlite3 *db,
VdbeCursor *pCsr,
int iFirst,
int *piNext
){
Pager *pPager = sqlite3BtreePager(pCsr->pBt);
VdbeSorter *pSorter = pCsr->pSorter;
int rc = SQLITE_OK;
int i;
int nMaxRef = (pSorter->nWorking * 9/10);
int N = 2;
int nIter; /* Number of iterators to initialize. */
assert( iFirst<pSorter->nOffset );
nIter = pSorter->nOffset - iFirst;
if( nIter>SORTER_MAX_MERGE_COUNT ){
nIter = SORTER_MAX_MERGE_COUNT;
}
assert( nIter>0 );
while( N<nIter ) N += N;
/* Allocate aIter[] and aTree[], if required. */
if( pSorter->aIter==0 ){
int nByte = N * (sizeof(int) + sizeof(VdbeSorterIter));
pSorter->aIter = (VdbeSorterIter *)sqlite3DbMallocZero(db, nByte);
if( !pSorter->aIter ) return SQLITE_NOMEM;
pSorter->aTree = (int *)&pSorter->aIter[N];
}
/* Initialize as many iterators as possible. */
for(i=iFirst;
rc==SQLITE_OK && i<pSorter->nOffset && (i-iFirst)<SORTER_MAX_MERGE_COUNT;
i++
){
int iIter = i - iFirst;
assert( iIter<=pSorter->nAlloc );
if( iIter==pSorter->nAlloc ){
rc = vdbeSorterGrowArrays(db, pSorter);
}
if( rc==SQLITE_OK ){
VdbeSorterIter *pIter = &pSorter->aIter[iIter];
i64 iStart = pSorter->aOffset[i];
i64 iEof;
if( i==(pSorter->nOffset-1) ){
iEof = pSorter->iWriteOff;
}else{
iEof = pSorter->aOffset[i+1];
}
rc = vdbeSorterIterInit(db, pSorter->pTemp1, iStart, iEof, pIter);
if( i>iFirst+1 ){
int nRef = (i-iFirst)*10;
if( nRef>=nMaxRef ){
i++;
break;
}
}
}
}
*piNext = i;
assert( i>iFirst );
while( (i-iFirst)>N ) N += N;
pSorter->nTree = N;
/* Populate the aTree[] array. */
for(i=N-1; rc==SQLITE_OK && i>0; i--){
rc = vdbeSorterDoCompare(pCsr, i);
}
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if( rc!=SQLITE_OK ) return rc;
if( pSorter->nOffset==0 ){
*pbEof = 1;
return SQLITE_OK;
}
while( rc==SQLITE_OK ){
int iRoot = 0;
int iNext = 0; /* Index of next segment to open */
int iNew = 0; /* Index of new, merged, PMA */
do {
/* This call configures iterators for merging. */
rc = vdbeSorterInitMerge(db, pCsr, iNext, &iNext);
assert( iNext>0 );
assert( rc!=SQLITE_OK || pSorter->aIter[ pSorter->aTree[1] ].pFile );
if( rc==SQLITE_OK && (iRoot>0 || iNext<pSorter->nOffset) ){
if( rc==SQLITE_OK && (iNew>0 || iNext<pSorter->nOffset) ){
int pgno;
int bEof = 0;
if( pTemp2==0 ){
rc = vdbeSorterOpenTempFile(db, &pTemp2);
}
if( rc==SQLITE_OK ){
pSorter->aOffset[iRoot] = iWrite2;
pSorter->aOffset[iNew] = iWrite2;
}
while( rc==SQLITE_OK && bEof==0 ){
int nByte;
VdbeSorterIter *pIter = &pSorter->aIter[ pSorter->aTree[1] ];
assert( pIter->pFile );
nByte = pIter->nKey + sqlite3VarintLen(pIter->nKey);
rc = sqlite3OsWrite(pTemp2, pIter->aAlloc, nByte, iWrite2);
iWrite2 += nByte;
if( rc==SQLITE_OK ){
rc = sqlite3VdbeSorterNext(db, pCsr, &bEof);
}
}
iRoot++;
iNew++;
}
}while( rc==SQLITE_OK && iNext<pSorter->nOffset );
if( iRoot==0 ){
if( iNew==0 ){
break;
}else{
sqlite3_file *pTmp = pSorter->pTemp1;
pSorter->nOffset = iRoot;
pSorter->nOffset = iNew;
pSorter->pTemp1 = pTemp2;
pTemp2 = pTmp;
pSorter->iWriteOff = iWrite2;
iWrite2 = 0;
}
}
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