serversel.cc

/*
    PowerMail versatile mail receiver
    Copyright (C) 2002  PowerDNS.COM BV

    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.

    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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/
#include "serversel.hh"
#include "megatalker.hh"
#include "logger.hh"
#include "argsettings.hh"
#include "common.hh"
#include <algorithm>
extern Logger L;


/** Use this to select the server that provides the most redundancy and has the highest priority. 
    Each server has a group and a priority. Servers within the same group do not provide mutual redundancy.

    Algorithm: make a list of groups with zero used servers and select a random group. 
    Within that group, randomize and stable sort, and take the first available server */

ServerSelect::ServerSelect(const vector<TargetData>&td)
{
  d_td=td; 
  for(td_t::iterator i=d_td.begin();i!=d_td.end();++i) 
    i->used=false;
}

static bool byPrio(const TargetData *a, const TargetData *b)
{
  static bool first=true;
  static bool favorEmpty;
  static bool favorLoad;

  if(first) {
    first=false;
    favorEmpty=args().switchSet("spread-disk");
    favorLoad=args().switchSet("spread-load");
  }
  
  if(a->priority < b->priority)
    return true;
  if(a->priority==b->priority && favorEmpty && (b->kbfree < a->kbfree)) // favour emtpier disks
    return true; 
  if(a->priority==b->priority && favorLoad && (a->load < b->load)) // favour lower load
    return true; 
  return false;
}

const TargetData *ServerSelect::getServer()
{
  map<int,vector<TargetData *> > perGroup;

  map<int,bool> usedGroup;
  for(td_t::iterator i=d_td.begin();i!=d_td.end();++i) {
    if(i->used) {
      usedGroup[i->group]=true;
    }
  }

  for(td_t::iterator i=d_td.begin();i!=d_td.end();++i) {
    if(i->up && !i->readonly && usedGroup[i->group]==false)
      perGroup[i->group].push_back(&*i);
  }

  if(perGroup.empty()) {
    L<<"No redundant servers left"<<endl;
    return 0;
  }
    
  int cGroup=random()%perGroup.size();

  map<int,vector<TargetData *> >::const_iterator i;
  int n=0;
  for(i=perGroup.begin();
      i!=perGroup.end();++i) 
    if(n++==cGroup)
      break;

  vector<TargetData *> candidates=i->second;
  if(candidates.empty()) { // should not happen
    L<<"Bummer, no servers! [this should not happen]"<<endl;
    exit(0); // die
  }

  random_shuffle(candidates.begin(),candidates.end());
  stable_sort(candidates.begin(),candidates.end(),byPrio);
  candidates[0]->used=true;
  return candidates[0];
}