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sqlite/ext/fts5/fts5_hash.c

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/*
** 2014 August 11
**
** The author disclaims copyright to this source code. In place of
** a legal notice, here is a blessing:
**
** May you do good and not evil.
** May you find forgiveness for yourself and forgive others.
** May you share freely, never taking more than you give.
**
******************************************************************************
**
*/
#ifdef SQLITE_ENABLE_FTS5
#include "fts5Int.h"
typedef struct Fts5HashEntry Fts5HashEntry;
/*
** This file contains the implementation of an in-memory hash table used
** to accumuluate "term -> doclist" content before it is flused to a level-0
** segment.
*/
struct Fts5Hash {
int *pnByte; /* Pointer to bytes counter */
int nEntry; /* Number of entries currently in hash */
int nSlot; /* Size of aSlot[] array */
Fts5HashEntry *pScan; /* Current ordered scan item */
Fts5HashEntry **aSlot; /* Array of hash slots */
};
/*
** Each entry in the hash table is represented by an object of the
** following type. Each object, its key (zKey[]) and its current data
** are stored in a single memory allocation. The position list data
** immediately follows the key data in memory.
**
** The data that follows the key is in a similar, but not identical format
** to the doclist data stored in the database. It is:
**
** * Rowid, as a varint
** * Position list, without 0x00 terminator.
** * Size of previous position list and rowid, as a 4 byte
** big-endian integer.
**
** iRowidOff:
** Offset of last rowid written to data area. Relative to first byte of
** structure.
**
** nData:
** Bytes of data written since iRowidOff.
*/
struct Fts5HashEntry {
Fts5HashEntry *pHashNext; /* Next hash entry with same hash-key */
Fts5HashEntry *pScanNext; /* Next entry in sorted order */
int nAlloc; /* Total size of allocation */
int iSzPoslist; /* Offset of space for 4-byte poslist size */
int nData; /* Total bytes of data (incl. structure) */
int iCol; /* Column of last value written */
int iPos; /* Position of last value written */
i64 iRowid; /* Rowid of last value written */
char zKey[0]; /* Nul-terminated entry key */
};
/*
** Allocate a new hash table.
*/
int sqlite3Fts5HashNew(Fts5Hash **ppNew, int *pnByte){
int rc = SQLITE_OK;
Fts5Hash *pNew;
*ppNew = pNew = (Fts5Hash*)sqlite3_malloc(sizeof(Fts5Hash));
if( pNew==0 ){
rc = SQLITE_NOMEM;
}else{
int nByte;
memset(pNew, 0, sizeof(Fts5Hash));
pNew->pnByte = pnByte;
pNew->nSlot = 1024;
nByte = sizeof(Fts5HashEntry*) * pNew->nSlot;
pNew->aSlot = (Fts5HashEntry**)sqlite3_malloc(nByte);
if( pNew->aSlot==0 ){
sqlite3_free(pNew);
*ppNew = 0;
rc = SQLITE_NOMEM;
}else{
memset(pNew->aSlot, 0, nByte);
}
}
return rc;
}
/*
** Free a hash table object.
*/
void sqlite3Fts5HashFree(Fts5Hash *pHash){
if( pHash ){
sqlite3Fts5HashClear(pHash);
sqlite3_free(pHash->aSlot);
sqlite3_free(pHash);
}
}
/*
** Empty (but do not delete) a hash table.
*/
void sqlite3Fts5HashClear(Fts5Hash *pHash){
int i;
for(i=0; i<pHash->nSlot; i++){
Fts5HashEntry *pNext;
Fts5HashEntry *pSlot;
for(pSlot=pHash->aSlot[i]; pSlot; pSlot=pNext){
pNext = pSlot->pHashNext;
sqlite3_free(pSlot);
}
}
memset(pHash->aSlot, 0, pHash->nSlot * sizeof(Fts5HashEntry*));
pHash->nEntry = 0;
}
static unsigned int fts5HashKey(int nSlot, const char *p, int n){
int i;
unsigned int h = 13;
for(i=n-1; i>=0; i--){
h = (h << 3) ^ h ^ p[i];
}
return (h % nSlot);
}
/*
** Resize the hash table by doubling the number of slots.
*/
static int fts5HashResize(Fts5Hash *pHash){
int nNew = pHash->nSlot*2;
int i;
Fts5HashEntry **apNew;
Fts5HashEntry **apOld = pHash->aSlot;
apNew = (Fts5HashEntry**)sqlite3_malloc(nNew*sizeof(Fts5HashEntry*));
if( !apNew ) return SQLITE_NOMEM;
memset(apNew, 0, nNew*sizeof(Fts5HashEntry*));
for(i=0; i<pHash->nSlot; i++){
while( apOld[i] ){
int iHash;
Fts5HashEntry *p = apOld[i];
apOld[i] = p->pHashNext;
iHash = fts5HashKey(nNew, p->zKey, strlen(p->zKey));
p->pHashNext = apNew[iHash];
apNew[iHash] = p;
}
}
sqlite3_free(apOld);
pHash->nSlot = nNew;
pHash->aSlot = apNew;
return SQLITE_OK;
}
static void fts5HashAddPoslistSize(Fts5HashEntry *p){
if( p->iSzPoslist ){
u8 *pPtr = (u8*)p;
int nSz = p->nData - p->iSzPoslist - 1;
if( nSz<=127 ){
pPtr[p->iSzPoslist] = nSz;
}else{
int nByte = sqlite3Fts5GetVarintLen((u32)nSz);
memmove(&pPtr[p->iSzPoslist + nByte], &pPtr[p->iSzPoslist + 1], nSz);
sqlite3PutVarint(&pPtr[p->iSzPoslist], nSz);
p->nData += (nByte-1);
}
p->iSzPoslist = 0;
}
}
int sqlite3Fts5HashWrite(
Fts5Hash *pHash,
i64 iRowid, /* Rowid for this entry */
int iCol, /* Column token appears in (-ve -> delete) */
int iPos, /* Position of token within column */
const char *pToken, int nToken /* Token to add or remove to or from index */
){
unsigned int iHash = fts5HashKey(pHash->nSlot, pToken, nToken);
Fts5HashEntry *p;
u8 *pPtr;
int nIncr = 0; /* Amount to increment (*pHash->pnByte) by */
/* Attempt to locate an existing hash entry */
for(p=pHash->aSlot[iHash]; p; p=p->pHashNext){
if( memcmp(p->zKey, pToken, nToken)==0 && p->zKey[nToken]==0 ) break;
}
/* If an existing hash entry cannot be found, create a new one. */
if( p==0 ){
int nByte = sizeof(Fts5HashEntry) + nToken + 1 + 64;
if( nByte<128 ) nByte = 128;
if( (pHash->nEntry*2)>=pHash->nSlot ){
int rc = fts5HashResize(pHash);
if( rc!=SQLITE_OK ) return rc;
iHash = fts5HashKey(pHash->nSlot, pToken, nToken);
}
p = (Fts5HashEntry*)sqlite3_malloc(nByte);
if( !p ) return SQLITE_NOMEM;
memset(p, 0, sizeof(Fts5HashEntry));
p->nAlloc = nByte;
memcpy(p->zKey, pToken, nToken);
p->zKey[nToken] = '\0';
p->nData = nToken + 1 + sizeof(Fts5HashEntry);
p->nData += sqlite3PutVarint(&((u8*)p)[p->nData], iRowid);
p->iSzPoslist = p->nData;
p->nData += 1;
p->iRowid = iRowid;
p->pHashNext = pHash->aSlot[iHash];
pHash->aSlot[iHash] = p;
pHash->nEntry++;
nIncr += p->nData;
}
/* Check there is enough space to append a new entry. Worst case scenario
** is:
**
** + 9 bytes for a new rowid,
** + 4 byte reserved for the "poslist size" varint.
** + 1 byte for a "new column" byte,
** + 3 bytes for a new column number (16-bit max) as a varint,
** + 5 bytes for the new position offset (32-bit max).
*/
if( (p->nAlloc - p->nData) < (9 + 4 + 1 + 3 + 5) ){
int nNew = p->nAlloc * 2;
Fts5HashEntry *pNew;
Fts5HashEntry **pp;
pNew = (Fts5HashEntry*)sqlite3_realloc(p, nNew);
if( pNew==0 ) return SQLITE_NOMEM;
pNew->nAlloc = nNew;
for(pp=&pHash->aSlot[iHash]; *pp!=p; pp=&(*pp)->pHashNext);
*pp = pNew;
p = pNew;
}
pPtr = (u8*)p;
nIncr -= p->nData;
/* If this is a new rowid, append the 4-byte size field for the previous
** entry, and the new rowid for this entry. */
if( iRowid!=p->iRowid ){
fts5HashAddPoslistSize(p);
p->nData += sqlite3PutVarint(&pPtr[p->nData], iRowid - p->iRowid);
p->iSzPoslist = p->nData;
p->nData += 1;
p->iCol = 0;
p->iPos = 0;
p->iRowid = iRowid;
}
if( iCol>=0 ){
/* Append a new column value, if necessary */
assert( iCol>=p->iCol );
if( iCol!=p->iCol ){
pPtr[p->nData++] = 0x01;
p->nData += sqlite3PutVarint(&pPtr[p->nData], iCol);
p->iCol = iCol;
p->iPos = 0;
}
/* Append the new position offset */
p->nData += sqlite3PutVarint(&pPtr[p->nData], iPos - p->iPos + 2);
p->iPos = iPos;
}
nIncr += p->nData;
*pHash->pnByte += nIncr;
return SQLITE_OK;
}
/*
** Arguments pLeft and pRight point to linked-lists of hash-entry objects,
** each sorted in key order. This function merges the two lists into a
** single list and returns a pointer to its first element.
*/
static Fts5HashEntry *fts5HashEntryMerge(
Fts5HashEntry *pLeft,
Fts5HashEntry *pRight
){
Fts5HashEntry *p1 = pLeft;
Fts5HashEntry *p2 = pRight;
Fts5HashEntry *pRet = 0;
Fts5HashEntry **ppOut = &pRet;
while( p1 || p2 ){
if( p1==0 ){
*ppOut = p2;
p2 = 0;
}else if( p2==0 ){
*ppOut = p1;
p1 = 0;
}else{
int i = 0;
while( p1->zKey[i]==p2->zKey[i] ) i++;
if( ((u8)p1->zKey[i])>((u8)p2->zKey[i]) ){
/* p2 is smaller */
*ppOut = p2;
ppOut = &p2->pScanNext;
p2 = p2->pScanNext;
}else{
/* p1 is smaller */
*ppOut = p1;
ppOut = &p1->pScanNext;
p1 = p1->pScanNext;
}
*ppOut = 0;
}
}
return pRet;
}
/*
** Extract all tokens from hash table iHash and link them into a list
** in sorted order. The hash table is cleared before returning. It is
** the responsibility of the caller to free the elements of the returned
** list.
*/
static int fts5HashEntrySort(
Fts5Hash *pHash,
const char *pTerm, int nTerm, /* Query prefix, if any */
Fts5HashEntry **ppSorted
){
const int nMergeSlot = 32;
Fts5HashEntry **ap;
Fts5HashEntry *pList;
int iSlot;
int i;
*ppSorted = 0;
ap = sqlite3_malloc(sizeof(Fts5HashEntry*) * nMergeSlot);
if( !ap ) return SQLITE_NOMEM;
memset(ap, 0, sizeof(Fts5HashEntry*) * nMergeSlot);
for(iSlot=0; iSlot<pHash->nSlot; iSlot++){
Fts5HashEntry *pIter;
for(pIter=pHash->aSlot[iSlot]; pIter; pIter=pIter->pHashNext){
if( pTerm==0 || 0==memcmp(pIter->zKey, pTerm, nTerm) ){
Fts5HashEntry *pEntry = pIter;
pEntry->pScanNext = 0;
for(i=0; ap[i]; i++){
pEntry = fts5HashEntryMerge(pEntry, ap[i]);
ap[i] = 0;
}
ap[i] = pEntry;
}
}
}
pList = 0;
for(i=0; i<nMergeSlot; i++){
pList = fts5HashEntryMerge(pList, ap[i]);
}
pHash->nEntry = 0;
sqlite3_free(ap);
*ppSorted = pList;
return SQLITE_OK;
}
/*
** Query the hash table for a doclist associated with term pTerm/nTerm.
*/
int sqlite3Fts5HashQuery(
Fts5Hash *pHash, /* Hash table to query */
const char *pTerm, int nTerm, /* Query term */
const char **ppDoclist, /* OUT: Pointer to doclist for pTerm */
int *pnDoclist /* OUT: Size of doclist in bytes */
){
unsigned int iHash = fts5HashKey(pHash->nSlot, pTerm, nTerm);
Fts5HashEntry *p;
for(p=pHash->aSlot[iHash]; p; p=p->pHashNext){
if( memcmp(p->zKey, pTerm, nTerm)==0 && p->zKey[nTerm]==0 ) break;
}
if( p ){
fts5HashAddPoslistSize(p);
*ppDoclist = &p->zKey[nTerm+1];
*pnDoclist = p->nData - (sizeof(*p) + nTerm + 1);
}else{
*ppDoclist = 0;
*pnDoclist = 0;
}
return SQLITE_OK;
}
int sqlite3Fts5HashScanInit(
Fts5Hash *p, /* Hash table to query */
const char *pTerm, int nTerm /* Query prefix */
){
return fts5HashEntrySort(p, pTerm, nTerm, &p->pScan);
}
void sqlite3Fts5HashScanNext(Fts5Hash *p){
Fts5HashEntry *pScan = p->pScan;
if( pScan ) p->pScan = pScan->pScanNext;
}
int sqlite3Fts5HashScanEof(Fts5Hash *p){
return (p->pScan==0);
}
void sqlite3Fts5HashScanEntry(
Fts5Hash *pHash,
const char **pzTerm, /* OUT: term (nul-terminated) */
const char **ppDoclist, /* OUT: pointer to doclist */
int *pnDoclist /* OUT: size of doclist in bytes */
){
Fts5HashEntry *p;
if( (p = pHash->pScan) ){
int nTerm = strlen(p->zKey);
fts5HashAddPoslistSize(p);
*pzTerm = p->zKey;
*ppDoclist = &p->zKey[nTerm+1];
*pnDoclist = p->nData - (sizeof(*p) + nTerm + 1);
}else{
*pzTerm = 0;
*ppDoclist = 0;
*pnDoclist = 0;
}
}
#endif /* SQLITE_ENABLE_FTS5 */
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