matcher/mergepostlist.cc

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/* mergepostlist.cc: MERGE of two posting lists
 *
 * Copyright 1999,2000,2001 BrightStation PLC
 * Copyright 2002 Ananova Ltd
 * Copyright 2002,2003,2004,2006 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
 */

#include <config.h>
#include "multimatch.h"
#include "emptypostlist.h"
#include "mergepostlist.h"
#include "branchpostlist.h"
#include "omassert.h"
#include "omdebug.h"
#include <xapian/errorhandler.h>

// NB don't prune - even with one sublist we still translate docids...

MergePostList::MergePostList(std::vector<PostList *> plists_,
                             MultiMatch *matcher_,
                             Xapian::ErrorHandler * errorhandler_)
        : plists(plists_), current(-1), matcher(matcher_),
          errorhandler(errorhandler_)
{
    DEBUGCALL(MATCH, void, "MergePostList::MergePostList", "std::vector<PostList *>");
}

MergePostList::~MergePostList()
{
    DEBUGCALL(MATCH, void, "MergePostList::~MergePostList", "");
    std::vector<PostList *>::const_iterator i;
    for (i = plists.begin(); i != plists.end(); i++) {
        delete *i;
    }
}

PostList *
MergePostList::next(Xapian::weight w_min)
{
    DEBUGCALL(MATCH, PostList *, "MergePostList::next", w_min);
    DEBUGLINE(MATCH, "current = " << current);
    if (current == -1) current = 0;
    while (true) {
        // FIXME: should skip over Remote matchers which aren't ready yet
        // and come back to them later...
        try {
            next_handling_prune(plists[current], w_min, matcher);
            if (!plists[current]->at_end()) break;
            current++;
        } catch (Xapian::Error & e) {
            if (errorhandler) {
                DEBUGLINE(EXCEPTION, "Calling error handler in MergePostList::next().");
                (*errorhandler)(e);
                // Continue match without this sub-postlist.
                delete plists[current];
                plists[current] = new EmptyPostList;
            } else {
                throw;
            }
        }
        if (unsigned(current) >= plists.size()) break;
        if (matcher) matcher->recalc_maxweight();
    }
    DEBUGLINE(MATCH, "current = " << current);
    RETURN(NULL);
}

PostList *
MergePostList::skip_to(Xapian::docid did, Xapian::weight w_min)
{
    DEBUGCALL(MATCH, PostList *, "MergePostList::skip_to", did << ", " << w_min);
    (void)did;
    (void)w_min;
    // MergePostList doesn't return documents in docid order, so skip_to
    // isn't a meaningful operation.
    throw Xapian::InvalidOperationError("MergePostList doesn't support skip_to");
}

Xapian::termcount
MergePostList::get_wdf() const
{
    DEBUGCALL(MATCH, Xapian::termcount, "MergePostList::get_wdf", "");
    RETURN(plists[current]->get_wdf());
}

Xapian::doccount
MergePostList::get_termfreq_max() const
{
    DEBUGCALL(MATCH, Xapian::doccount, "MergePostList::get_termfreq_max", "");
    // sum of termfreqs for all children
    Xapian::doccount total = 0;
    vector<PostList *>::const_iterator i;
    for (i = plists.begin(); i != plists.end(); i++) {
        total += (*i)->get_termfreq_max();
    }
    return total;
}

Xapian::doccount
MergePostList::get_termfreq_min() const
{
    DEBUGCALL(MATCH, Xapian::doccount, "MergePostList::get_termfreq_min", "");
    // sum of termfreqs for all children
    Xapian::doccount total = 0;
    vector<PostList *>::const_iterator i;
    for (i = plists.begin(); i != plists.end(); i++) {
        total += (*i)->get_termfreq_min();
    }
    return total;
}

Xapian::doccount
MergePostList::get_termfreq_est() const
{
    DEBUGCALL(MATCH, Xapian::doccount, "MergePostList::get_termfreq_est", "");
    // sum of termfreqs for all children
    Xapian::doccount total = 0;
    vector<PostList *>::const_iterator i;
    for (i = plists.begin(); i != plists.end(); i++) {
        total += (*i)->get_termfreq_est();
    }
    return total;
}

Xapian::docid
MergePostList::get_docid() const
{
    DEBUGCALL(MATCH, Xapian::docid, "MergePostList::get_docid", "");
    Assert(current != -1);
    // FIXME: this needs fixing so we can prune plists - see MultiPostlist
    // for code which does this...
    RETURN((plists[current]->get_docid() - 1) * plists.size() + current + 1);
}

Xapian::weight
MergePostList::get_weight() const
{
    DEBUGCALL(MATCH, Xapian::weight, "MergePostList::get_weight", "");
    Assert(current != -1);
    return plists[current]->get_weight();
}

const string *
MergePostList::get_collapse_key() const
{
    DEBUGCALL(MATCH, string *, "MergePostList::get_collapse_key", "");
    Assert(current != -1);
    return plists[current]->get_collapse_key();
}

Xapian::weight
MergePostList::get_maxweight() const
{
    DEBUGCALL(MATCH, Xapian::weight, "MergePostList::get_maxweight", "");
    return w_max;
}

Xapian::weight
MergePostList::recalc_maxweight()
{
    DEBUGCALL(MATCH, Xapian::weight, "MergePostList::recalc_maxweight", "");
    w_max = 0;
    vector<PostList *>::iterator i;
    for (i = plists.begin(); i != plists.end(); i++) {
        try {
            Xapian::weight w = (*i)->recalc_maxweight();
            if (w > w_max) w_max = w;
        } catch (Xapian::Error & e) {
            if (errorhandler) {
                DEBUGLINE(EXCEPTION, "Calling error handler in MergePostList::recalc_maxweight().");
                (*errorhandler)(e);

                if (current == i - plists.begin()) {
                    // Fatal error
                    throw;
                }
                // Continue match without this sub-postlist.
                delete (*i);
                *i = new EmptyPostList;
            } else {
                throw;
            }
        }
    }
    return w_max;
}

bool
MergePostList::at_end() const
{
    DEBUGCALL(MATCH, bool, "MergePostList::at_end", "");
    Assert(current != -1);
    return unsigned(current) >= plists.size();    
}

string
MergePostList::get_description() const
{
    string desc = "( Merge ";
    vector<PostList *>::const_iterator i;
    for (i = plists.begin(); i != plists.end(); i++) {
        desc += (*i)->get_description() + " ";
    }
    return desc + ")";
}

Xapian::doclength
MergePostList::get_doclength() const
{
    DEBUGCALL(MATCH, Xapian::doclength, "MergePostList::get_doclength", "");
    Assert(current != -1);
    return plists[current]->get_doclength();
}

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