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Further apropos(1) speed optimization was trickier than anticipated.
Contrary to what i initially thought, almost all time is now spent
inside sqlite3(3) routines, and i found no easy way calling less of them.
However, sqlite(3) spends substantial time in malloc(3), and even more
(twice that) in its immediate malloc wrapper, sqlite3MemMalloc(),
keeping track of all individual malloc chunk sizes.  Typically about
90% of the malloced memory is used for purposes of the pagecache.

By providing an mmap(3) MAP_ANON SQLITE_CONFIG_PAGECACHE, execution
time decreases by 20-25% for simple (Nd and/or Nm) queries, 10-20% for
non-NAME queries, and even apropos(1) resident memory size as reported
by top(1) decreases by 20% for simple and by 60% for non-NAME queries.
The new function, mansearch_setup(), spends no measurable time.

The pagesize chosen is optimal:
* Substantially smaller pages yield no gain at all.
* Larger pages provide no additional benefit and just waste memory.

The chosen number of pages in the cache is a compromise:
* For simple queries, a handful of pages would suffice to get the full
speed effect, at an apropos(1) resident memory size of about 2.0 MB.
* For non-NAME queries, a large pagecache with 2k pages (2.5 MB) might
gain a few more percent in speed, but at the expense of doubling the
apropos(1) resident memory size for *all* queries.
* The chosen number of 256 pages (330 kB) allows nearly full speed gain
for all queries at the price of a 15% resident memory size increase.

/*	$Id: apropos.c,v 1.38 2014/04/11 15:46:52 schwarze Exp $ */
/*
 * Copyright (c) 2012 Kristaps Dzonsons <kristaps@bsd.lv>
 * Copyright (c) 2013 Ingo Schwarze <schwarze@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <sys/param.h>

#include <assert.h>
#include <getopt.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "manpath.h"
#include "mansearch.h"

int
main(int argc, char *argv[])
{
	int		 ch, whatis;
	struct mansearch search;
	size_t		 i, sz;
	struct manpage	*res;
	struct manpaths	 paths;
	char		*defpaths, *auxpaths;
	char		*conf_file;
	char		*progname;
	const char	*outkey;
	extern char	*optarg;
	extern int	 optind;

	progname = strrchr(argv[0], '/');
	if (progname == NULL)
		progname = argv[0];
	else
		++progname;

	whatis = (0 == strncmp(progname, "whatis", 6));

	memset(&paths, 0, sizeof(struct manpaths));
	memset(&search, 0, sizeof(struct mansearch));

	auxpaths = defpaths = NULL;
	conf_file = NULL;
	outkey = "Nd";

	while (-1 != (ch = getopt(argc, argv, "C:M:m:O:S:s:")))
		switch (ch) {
		case ('C'):
			conf_file = optarg;
			break;
		case ('M'):
			defpaths = optarg;
			break;
		case ('m'):
			auxpaths = optarg;
			break;
		case ('O'):
			outkey = optarg;
			break;
		case ('S'):
			search.arch = optarg;
			break;
		case ('s'):
			search.sec = optarg;
			break;
		default:
			goto usage;
		}

	argc -= optind;
	argv += optind;

	if (0 == argc)
		goto usage;

	search.deftype = whatis ? TYPE_Nm : TYPE_Nm | TYPE_Nd;
	search.flags = whatis ? MANSEARCH_WHATIS : 0;

	manpath_parse(&paths, conf_file, defpaths, auxpaths);
	mansearch_setup(1);
	ch = mansearch(&search, &paths, argc, argv, outkey, &res, &sz);
	manpath_free(&paths);

	if (0 == ch)
		goto usage;

	for (i = 0; i < sz; i++) {
		printf("%s - %s\n", res[i].names,
		    NULL == res[i].output ? "" : res[i].output);
		free(res[i].file);
		free(res[i].names);
		free(res[i].output);
	}

	free(res);
	mansearch_setup(0);
	return(sz ? EXIT_SUCCESS : EXIT_FAILURE);
usage:
	fprintf(stderr, "usage: %s [-C file] [-M path] [-m path] "
			"[-O outkey] "
			"[-S arch] [-s section]%s ...\n", progname,
			whatis ? " name" : "\n               expression");
	return(EXIT_FAILURE);
}