SQLite

      if( rc==SQLITE_ERROR ){
        p->base.zErrMsg = sqlite3_mprintf("malformed MATCH expression: [%s]",
                                          zQuery);
      }
      return rc;
    }

    rc = sqlite3Fts3ReadLock(p);
    if( rc!=SQLITE_OK ) return rc;

    rc = evalFts3Expr(p, pCsr->pExpr, &pCsr->aDoclist, &pCsr->nDoclist, 0);
    pCsr->pNextId = pCsr->aDoclist;
    pCsr->iPrevId = 0;
  }

  if( rc!=SQLITE_OK ) return rc;
  return fts3NextMethod(pCursor);

  Fts3Table *, Fts3SegReader **, int, Fts3SegFilter *,
  int (*)(Fts3Table *, void *, char *, int, char *, int),  void *
);
int sqlite3Fts3ReadBlock(Fts3Table*, sqlite3_int64, char const**, int*);
int sqlite3Fts3AllSegdirs(Fts3Table*, sqlite3_stmt **);
int sqlite3Fts3MatchinfoDocsizeLocal(Fts3Cursor*, u32*);
int sqlite3Fts3MatchinfoDocsizeGlobal(Fts3Cursor*, u32*);
int sqlite3Fts3ReadLock(Fts3Table *);

/* Flags allowed as part of the 4th argument to SegmentReaderIterate() */
#define FTS3_SEGMENT_REQUIRE_POS   0x00000001
#define FTS3_SEGMENT_IGNORE_EMPTY  0x00000002
#define FTS3_SEGMENT_COLUMN_FILTER 0x00000004
#define FTS3_SEGMENT_PREFIX        0x00000008

    *pzBlock = (char *)sqlite3_column_blob(pStmt, 0);
    if( sqlite3_column_type(pStmt, 0)!=SQLITE_BLOB ){
      return SQLITE_CORRUPT;
    }
  }
  return SQLITE_OK;
}

/*
** This function ensures that the caller has obtained a shared-cache
** table-lock on the %_content table. This is required before reading
** data from the fts3 table. If this lock is not acquired first, then
** the caller may end up holding read-locks on the %_segments and %_segdir
** tables, but no read-lock on the %_content table. If this happens 
** a second connection will be able to write to the fts3 table, but
** attempting to commit those writes might return SQLITE_LOCKED or
** SQLITE_LOCKED_SHAREDCACHE (because the commit attempts to obtain 
** write-locks on the %_segments and %_segdir ** tables). 
**
** We try to avoid this because if FTS3 returns any error when committing
** a transaction, the whole transaction will be rolled back. And this is
** not what users expect when they get SQLITE_LOCKED_SHAREDCACHE. It can
** still happen if the user reads data directly from the %_segments or
** %_segdir tables instead of going through FTS3 though.
*/
int sqlite3Fts3ReadLock(Fts3Table *p){
  int rc;                         /* Return code */
  sqlite3_stmt *pStmt;            /* Statement used to obtain lock */

  rc = fts3SqlStmt(p, SQL_SELECT_CONTENT_BY_ROWID, &pStmt, 0);
  if( rc==SQLITE_OK ){
    sqlite3_bind_null(pStmt, 1);
    sqlite3_step(pStmt);
    rc = sqlite3_reset(pStmt);
  }
  return rc;
}

/*
** Set *ppStmt to a statement handle that may be used to iterate through
** all rows in the %_segdir table, from oldest to newest. If successful,
** return SQLITE_OK. If an error occurs while preparing the statement, 
** return an SQLite error code.
**