root / tags / 1.0.8 / xapian-core / backends / flint / flint_postlist.h

/* flint_postlist.h: Postlists in flint databases
 *
 * Copyright 1999,2000,2001 BrightStation PLC
 * Copyright 2002 Ananova Ltd
 * Copyright 2002,2003,2004,2005,2007 Olly Betts
 * Copyright 2007 Lemur Consulting Ltd
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301
 * USA
 */

#ifndef OM_HGUARD_FLINT_POSTLIST_H
#define OM_HGUARD_FLINT_POSTLIST_H

#include <xapian/database.h>

#include "flint_types.h"
#include "flint_positionlist.h"
#include "leafpostlist.h"
#include "omassert.h"
#include "omdebug.h"

#include "autoptr.h"
#include <map>
#include <string>

using namespace std;

class FlintCursor;
class FlintDatabase;

class PostlistChunkReader;
class PostlistChunkWriter;

class FlintPostListTable : public FlintTable {
    public:
        /** Create a new table object.
         *
         *  This does not create the table on disk - the create() method must
         *  be called before the table is created on disk
         *
         *  This also does not open the table - the open() method must be
         *  called before use is made of the table.
         *
         *  @param path_          - Path at which the table is stored.
         *  @param readonly_      - whether to open the table for read only
         *                          access.
         */
        FlintPostListTable(string path_, bool readonly_)
            : FlintTable(path_ + "/postlist.", readonly_) { }

        /// Merge added, removed, and changed entries.
        void merge_changes(
            const map<string, map<Xapian::docid, pair<char, Xapian::termcount> > > & mod_plists,
            const map<Xapian::docid, Xapian::termcount> & doclens,
            const map<string, pair<Xapian::termcount_diff, Xapian::termcount_diff> > & freq_deltas);

        Xapian::docid get_chunk(const string &tname,
                Xapian::docid did, bool adding,
                PostlistChunkReader ** from, PostlistChunkWriter **to);

        /// Compose a key from a termname and docid.
        static string make_key(const string & term, Xapian::docid did) {
            string key = pack_string_preserving_sort(term);
            key += pack_uint_preserving_sort(did);
            return key;
        }

        /// Compose a key from a termname.
        static string make_key(const string & term) {
            return pack_string_preserving_sort(term);
        }

        bool term_exists(const string & term) const {
            return key_exists(make_key(term));
        }

        /** Returns number of docs indexed by @a term.
         *
         *  This is the length of the postlist.
         */
        Xapian::doccount get_termfreq(const std::string & term) const;

        /** Returns the number of occurrences of @a term in the database.
         *
         *  This is the sum of the wdfs in the postlist.
         */
        Xapian::termcount get_collection_freq(const std::string & term) const;
};

/** A postlist in a flint database.
 */
class FlintPostList : public LeafPostList {
   protected: // FlintModifiedPostList needs to access these.
        /** The database we are searching.  This pointer is held so that the
         *  database doesn't get deleted before us, and also to give us access
         *  to the position_table.
         */
        Xapian::Internal::RefCntPtr<const FlintDatabase> this_db;

        /// The termname for this postlist.
        string tname;

        /// Whether we've started reading the list yet.
        bool have_started;

        /// The position list object for this posting list.
        FlintPositionList positionlist;

    private:
        /// Cursor pointing to current chunk of postlist.
        AutoPtr<FlintCursor> cursor;

        /// True if this is the last chunk.
        bool is_last_chunk;

        /// The first document id in this chunk.
        Xapian::docid first_did_in_chunk;

        /// The last document id in this chunk.
        Xapian::docid last_did_in_chunk;

        /// Position of iteration through current chunk.
        const char * pos;

        /// Pointer to byte after end of current chunk.
        const char * end;

        /// Document id we're currently at.
        Xapian::docid did;

        /// The (absolute) length of the current document.
        flint_doclen_t doclength;

        /// The wdf of the current document.
        Xapian::termcount wdf;

        /// Whether we've run off the end of the list yet.
        bool is_at_end;

        /// The number of entries in the posting list.
        Xapian::doccount number_of_entries;

        /// Copying is not allowed.
        FlintPostList(const FlintPostList &);

        /// Assignment is not allowed.
        void operator=(const FlintPostList &);

        /** Move to the next item in the chunk, if possible.
         *  If already at the end of the chunk, returns false.
         */
        bool next_in_chunk();

        /** Move to the next chunk.
         *
         *  If there are no more chunks in this postlist, this will set
         *  is_at_end to true.
         */
        void next_chunk();

        /** Return true if the given document ID lies in the range covered
         *  by the current chunk.  This does not say whether the document ID
         *  is actually present.  It will return false if the document ID
         *  is greater than the last document ID in the chunk, even if it is
         *  less than the first document ID in the next chunk: it is possible
         *  for no chunk to contain a particular document ID.
         */
        bool current_chunk_contains(Xapian::docid desired_did);

        /** Move to chunk containing the specified document ID.
         *
         *  This moves to the chunk whose starting document ID is
         *  <= desired_did, but such that the next chunk's starting
         *  document ID is > desired_did.
         *
         *  It is thus possible that current_chunk_contains(desired_did)
         *  will return false after this call, since the document ID
         *  might lie after the end of this chunk, but before the start
         *  of the next chunk.
         */
        void move_to_chunk_containing(Xapian::docid desired_did);

        /** Scan forward in the current chunk for the specified document ID.
         *
         *  This is particularly efficient if the desired document ID is
         *  greater than the last in the chunk - it then skips straight
         *  to the end.
         *
         *  @return true if we moved to a valid document,
         *          false if we reached the end of the chunk.
         */
        bool move_forward_in_chunk_to_at_least(Xapian::docid desired_did);

    public:
        /// Default constructor.
        FlintPostList(Xapian::Internal::RefCntPtr<const FlintDatabase> this_db_,
                      const string & tname);

        /// Destructor.
        ~FlintPostList();

        /** Returns number of docs indexed by this term.
         *
         *  This is the length of the postlist.
         */
        Xapian::doccount get_termfreq() const { return number_of_entries; }

        /// Returns the current docid.
        Xapian::docid get_docid() const { Assert(have_started); return did; }

        /// Returns the length of current document.
        Xapian::doclength get_doclength() const {
            DEBUGCALL(DB, Xapian::doclength, "FlintPostList::get_doclength", "");
            Assert(have_started);
            RETURN(static_cast<Xapian::doclength>(doclength));
        }

        /** Returns the Within Document Frequency of the term in the current
         *  document.
         */
        Xapian::termcount get_wdf() const { Assert(have_started); return wdf; }

        /** Get the list of positions of the term in the current document.
         */
        PositionList *read_position_list();

        /** Get the list of positions of the term in the current document.
         */
        PositionList * open_position_list() const;

        /// Move to the next document.
        PostList * next(Xapian::weight w_min);

        /// Skip to next document with docid >= docid.
        PostList * skip_to(Xapian::docid desired_did, Xapian::weight w_min);

        /// Return true if and only if we're off the end of the list.
        bool at_end() const { return is_at_end; }

        /// Get a description of the document.
        std::string get_description() const;

        /// Read the number of entries and the collection frequency.
        static void read_number_of_entries(const char ** posptr,
                                           const char * end,
                                           Xapian::termcount * number_of_entries_ptr,
                                           Xapian::termcount * collection_freq_ptr);
};

#endif /* OM_HGUARD_FLINT_POSTLIST_H */