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/** @file chert_dbstats.cc
* @brief Chert class for database statistics.
*/
/* Copyright (C) 2009 Olly Betts
*
* 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 "chert_dbstats.h"
#include "chert_postlist.h"
using namespace std;
/// The key in the postlist table which we use to store our encoded statistics.
static const string DATABASE_STATS_KEY(1, '\0');
void
ChertDatabaseStats::read(ChertPostListTable & postlist_table)
{
string data;
if (!postlist_table.get_exact_entry(DATABASE_STATS_KEY, data)) {
// If there's no entry yet, then all the values are zero.
total_doclen = 0;
last_docid = 0;
doclen_lbound = 0;
doclen_ubound = 0;
wdf_ubound = 0;
return;
}
const char * p = data.data();
const char * end = p + data.size();
if (unpack_uint(&p, end, &last_docid) &&
unpack_uint(&p, end, &doclen_lbound) &&
unpack_uint(&p, end, &wdf_ubound) &&
unpack_uint(&p, end, &doclen_ubound) &&
unpack_uint_last(&p, end, &total_doclen)) {
// doclen_ubound should always be >= wdf_ubound, so we store the
// difference as it may encode smaller. wdf_ubound is likely to
// be larger than doclen_lbound.
doclen_ubound += wdf_ubound;
return;
}
if (p)
throw Xapian::DatabaseCorruptError("Bad encoded DB stats (overflowed)");
throw Xapian::DatabaseCorruptError("Bad encoded DB stats (out of data)");
}
void
ChertDatabaseStats::write(ChertPostListTable & postlist_table) const
{
string data;
pack_uint(data, last_docid);
pack_uint(data, doclen_lbound);
pack_uint(data, wdf_ubound);
// doclen_ubound should always be >= wdf_ubound, so we store the
// difference as it may encode smaller. wdf_ubound is likely to
// be larger than doclen_lbound.
pack_uint(data, doclen_ubound - wdf_ubound);
// Micro-optimisation: total_doclen is likely to be the largest value, so
// store it last as pack_uint_last() uses a slightly more compact encoding
// - this could save us a few bytes!
pack_uint_last(data, total_doclen);
postlist_table.add(DATABASE_STATS_KEY, data);
}
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