DBD-SQLite
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SQLITE_PRIVATE void sqlite3BtreeGetMeta(Btree *pBtree, int idx, u32 *pValue);
SQLITE_PRIVATE int sqlite3BtreeUpdateMeta(Btree*, int idx, u32 value);
SQLITE_PRIVATE int sqlite3BtreeNewDb(Btree *p);
/*
** The second parameter to sqlite3BtreeGetMeta or sqlite3BtreeUpdateMeta
** should be one of the following values. The integer values are assigned
** to constants so that the offset of the corresponding field in an
** SQLite database header may be found using the following formula:
**
** offset = 36 + (idx * 4)
**
** For example, the free-page-count field is located at byte offset 36 of
** the database file header. The incr-vacuum-flag field is located at
** byte offset 64 (== 36+4*7).
**
** The BTREE_DATA_VERSION value is not really a value stored in the header.
** It is a read-only number computed by the pager. But we merge it with
** the header value access routines since its access pattern is the same.
/*
** Parameter aData must point to a buffer of pPager->pageSize bytes
** of data. Compute and return a checksum based on the contents of the
** page of data and the current value of pPager->cksumInit.
**
** This is not a real checksum. It is really just the sum of the
** random initial value (pPager->cksumInit) and every 200th byte
** of the page data, starting with byte offset (pPager->pageSize%200).
** Each byte is interpreted as an 8-bit unsigned integer.
**
** Changing the formula used to compute this checksum results in an
** incompatible journal file format.
**
** If journal corruption occurs due to a power failure, the most likely
** scenario is that one end or the other of the record will be changed.
** It is much less likely that the two ends of the journal record will be
** correct and the middle be corrupt. Thus, this "checksum" scheme,
** though fast and simple, catches the mostly likely kind of corruption.
*/
static u32 pager_cksum(Pager *pPager, const u8 *aData){
u32 cksum = pPager->cksumInit; /* Checksum value to return */
**
** N between YY_MIN_REDUCE Reduce by rule N-YY_MIN_REDUCE
** and YY_MAX_REDUCE
**
** The action table is constructed as a single large table named yy_action[].
** Given state S and lookahead X, the action is computed as either:
**
** (A) N = yy_action[ yy_shift_ofst[S] + X ]
** (B) N = yy_default[S]
**
** The (A) formula is preferred. The B formula is used instead if
** yy_lookahead[yy_shift_ofst[S]+X] is not equal to X.
**
** The formulas above are for computing the action when the lookahead is
** a terminal symbol. If the lookahead is a non-terminal (as occurs after
** a reduce action) then the yy_reduce_ofst[] array is used in place of
** the yy_shift_ofst[] array.
**
** The following are the tables generated in this section:
**
** yy_action[] A single table containing all actions.
** yy_lookahead[] A table containing the lookahead for each entry in
** yy_action. Used to detect hash collisions.
** yy_shift_ofst[] For each state, the offset into yy_action for
};
/*
** RBU handle.
**
** nPhaseOneStep:
** If the RBU database contains an rbu_count table, this value is set to
** a running estimate of the number of b-tree operations required to
** finish populating the *-oal file. This allows the sqlite3_bp_progress()
** API to calculate the permyriadage progress of populating the *-oal file
** using the formula:
**
** permyriadage = (10000 * nProgress) / nPhaseOneStep
**
** nPhaseOneStep is initialized to the sum of:
**
** nRow * (nIndex + 1)
**
** for all source tables in the RBU database, where nRow is the number
** of rows in the source table and nIndex the number of indexes on the
** corresponding target database table.
**
** N between fts5YY_MIN_REDUCE Reduce by rule N-fts5YY_MIN_REDUCE
** and fts5YY_MAX_REDUCE
**
** The action table is constructed as a single large table named fts5yy_action[].
** Given state S and lookahead X, the action is computed as either:
**
** (A) N = fts5yy_action[ fts5yy_shift_ofst[S] + X ]
** (B) N = fts5yy_default[S]
**
** The (A) formula is preferred. The B formula is used instead if
** fts5yy_lookahead[fts5yy_shift_ofst[S]+X] is not equal to X.
**
** The formulas above are for computing the action when the lookahead is
** a terminal symbol. If the lookahead is a non-terminal (as occurs after
** a reduce action) then the fts5yy_reduce_ofst[] array is used in place of
** the fts5yy_shift_ofst[] array.
**
** The following are the tables generated in this section:
**
** fts5yy_action[] A single table containing all actions.
** fts5yy_lookahead[] A table containing the lookahead for each entry in
** fts5yy_action. Used to detect hash collisions.
** fts5yy_shift_ofst[] For each state, the offset into fts5yy_action for
assert( rc!=SQLITE_OK || nRow>0 );
if( rc==SQLITE_OK ) rc = pApi->xColumnTotalSize(pFts, -1, &nToken);
if( rc==SQLITE_OK ) p->avgdl = (double)nToken / (double)nRow;
/* Calculate an IDF for each phrase in the query */
for(i=0; rc==SQLITE_OK && i<nPhrase; i++){
sqlite3_int64 nHit = 0;
rc = pApi->xQueryPhrase(pFts, i, (void*)&nHit, fts5CountCb);
if( rc==SQLITE_OK ){
/* Calculate the IDF (Inverse Document Frequency) for phrase i.
** This is done using the standard BM25 formula as found on wikipedia:
**
** IDF = log( (N - nHit + 0.5) / (nHit + 0.5) )
**
** where "N" is the total number of documents in the set and nHit
** is the number that contain at least one instance of the phrase
** under consideration.
**
** The problem with this is that if (N < 2*nHit), the IDF is
** negative. Which is undesirable. So the mimimum allowable IDF is
** (1e-6) - roughly the same as a term that appears in just over
/*
** Implementation of bm25() function.
*/
static void fts5Bm25Function(
const Fts5ExtensionApi *pApi, /* API offered by current FTS version */
Fts5Context *pFts, /* First arg to pass to pApi functions */
sqlite3_context *pCtx, /* Context for returning result/error */
int nVal, /* Number of values in apVal[] array */
sqlite3_value **apVal /* Array of trailing arguments */
){
const double k1 = 1.2; /* Constant "k1" from BM25 formula */
const double b = 0.75; /* Constant "b" from BM25 formula */
int rc; /* Error code */
double score = 0.0; /* SQL function return value */
Fts5Bm25Data *pData; /* Values allocated/calculated once only */
int i; /* Iterator variable */
int nInst = 0; /* Value returned by xInstCount() */
double D = 0.0; /* Total number of tokens in row */
double *aFreq = 0; /* Array of phrase freq. for current row */
/* Calculate the phrase frequency (symbol "f(qi,D)" in the documentation)
** for each phrase in the query for the current row. */
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