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boinc/ssim/ssim.cpp

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// This file is part of BOINC.
// http://boinc.berkeley.edu
// Copyright (C) 2011 University of California
//
// BOINC is free software; you can redistribute it and/or modify it
// under the terms of the GNU Lesser General Public License
// as published by the Free Software Foundation,
// either version 3 of the License, or (at your option) any later version.
//
// BOINC 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 Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with BOINC. If not, see <http://www.gnu.org/licenses/>.
// ssim - simulator for distributed storage
//
// Simulates the storage of files on a dynamic set of hosts.
//
// The model of the host population is:
// - hosts arrival is a Poisson process
// - host lifetime is exponentially distributed
// - the time needed to download n bytes of data to/from a host is
// U()*n/DOWNLOAD_BYTES_SEC
// where U() is a uniform random var
// TODO: add a factor corresponding to host availability
#define HOSTS_PER_DAY 10.
#define HOST_LIFE_MEAN 100.*86400
#define UPLOAD_BYTES_SEC (5./3600)
#define DOWNLOAD_BYTES_SEC (5./3600)
// We simulate policies based on coding and replication.
//
// Coding means that data is divided into M = N+K units,
// of which any N are sufficient to reconstruct the original data.
// When we need to reconstruct an encoded unit on the server,
// we try to upload N_UPLOAD subunits,
// where N <= N_UPLOAD <= M
#define ENCODING_N 4
#define ENCODING_K 2
#define ENCODING_M 6
#define N_UPLOAD 5
// The units in an encoding can themselves be encoded.
// There are LEVELS levels of encoding.
#define ENCODING_LEVELS 1
// The bottom-level data units ("chunks") are stored on hosts,
// possibly with replication
#define REPLICATION_LEVEL 2
// Terminology:
//
// A data unit is "recoverable" if it can be recovered on the server
// by uploading data from hosts.
// A chunk is recoverable if it's present on the server or on at least 1 host.
// (note: if it's downloading, it's still present on the server)
// An encoded data unit is recoverable if at least N
// of its subunits are recoverable.
// Figures of merit
//
// for each file, we compute:
// - the average and peak server network rate, up and down
// - the average and peak disk usage
// - the average and min fault tolerance level
// (i.e. number of simultaneous host failures needed to lose the file)
//
// These are measured starting from the time when the file's
// initial downloads have all succeeded or failed
#include <math.h>
#include <limits.h>
#include <stdio.h>
#include <set>
#include "des.h"
using std::set;
#define EVENT_DEBUG
#define SAMPLE_DEBUG
//#define RECOVERY_DEBUG
SIMULATOR sim;
int next_file_id=0;
int next_host_id=0;
inline double drand() {
return (double)rand()/(double)RAND_MAX;
}
double ran_exp(double mean) {
return -log(drand())*mean;
}
char* time_str(double t) {
static char buf[256];
struct tm;
int n = (int)t;
int nsec = n % 60;
n /= 60;
int nmin = n % 60;
n /= 60;
int nhour = n % 24;
n /= 24;
sprintf(buf, "%4d days %02d:%02d:%02d", n, nhour, nmin, nsec);
return buf;
}
char* now_str() {
return time_str(sim.now);
}
struct CHUNK;
struct CHUNK_ON_HOST;
struct META_CHUNK;
struct DFILE;
struct HOST;
set<HOST*> hosts;
// Represents a host.
// The associated EVENT is the disappearance of the host
//
struct HOST : public EVENT {
int id;
set<CHUNK_ON_HOST*> chunks; // chunks present or downloading
virtual void handle();
HOST() {
t = sim.now + ran_exp(HOST_LIFE_MEAN);
id = next_host_id++;
hosts.insert(this);
}
};
// The host arrival process.
// The associated EVENT is the arrival of a host
//
struct HOST_ARRIVAL : public EVENT {
virtual void handle() {
sim.insert(new HOST);
t += ran_exp(86400./HOSTS_PER_DAY);
sim.insert(this);
}
};
void die(const char* msg) {
printf("%s: %s\n", now_str(), msg);
exit(1);
}
// The status of a chunk on a particular host.
// The associated event is the completion of an upload or download
//
struct CHUNK_ON_HOST : public EVENT {
HOST* host;
CHUNK* chunk;
char name[256];
bool present_on_host;
bool transfer_in_progress; // upload if present_on_host, else download
virtual void handle();
inline bool download_in_progress() {
return (transfer_in_progress && !present_on_host);
}
};
#define PRESENT 0
#define RECOVERABLE 1
#define UNRECOVERABLE 2
// base class for chunks and meta-chunks
//
struct DATA_UNIT {
virtual void recovery_plan(){};
virtual void recovery_action(){};
int status;
bool in_recovery_set;
bool data_now_present;
bool data_needed;
double cost;
int fault_tolerance;
// min # of host failures that would make this unrecoverable
char name[64];
};
struct CHUNK : DATA_UNIT {
set<CHUNK_ON_HOST*> hosts;
META_CHUNK* parent;
double size;
bool present_on_server;
CHUNK(META_CHUNK* mc, double s, int index);
void start_upload();
void host_failed(CHUNK_ON_HOST* p);
bool download_in_progress();
void upload_complete();
void download_complete();
void assign();
virtual void recovery_plan();
virtual void recovery_action();
};
struct META_CHUNK : DATA_UNIT {
vector<DATA_UNIT*> children;
META_CHUNK* parent;
int n_children_present;
bool have_unrecoverable_children;
DFILE* dfile;
bool uploading;
META_CHUNK(
DFILE* d, META_CHUNK* par, double size, int encoding_level, int index
);
virtual void recovery_plan();
virtual void recovery_action();
};
// keeps track of a time-varying property of a file
// (server disk usage, up/download rate, fault tolerance level)
//
struct STATS_ITEM {
double value;
double integral;
double max_val;
double max_val_time;
double prev_t;
double start_time;
bool first;
STATS_ITEM() {
value = 0;
integral = 0;
max_val = 0;
max_val_time = 0;
first = true;
}
void sample(double v, bool collecting_stats) {
double old_val = value;
value = v;
if (!collecting_stats) return;
if (first) {
first = false;
prev_t = sim.now;
return;
}
double dt = sim.now - prev_t;
prev_t = sim.now;
integral += dt*old_val;
if (v > max_val) {
max_val = v;
max_val_time = sim.now;
}
}
void sample_inc(double inc, bool collecting_stats) {
sample(value+inc, collecting_stats);
#ifdef SAMPLE_DEBUG
printf("%s: sample_inc: %f %f\n", now_str(), inc, value);
#endif
}
void print() {
sample_inc(0, true);
double dt = sim.now - start_time;
printf(" mean: %f\n", integral/dt);
printf(" max: %f\n", max_val);
printf(" time of max: %s\n", time_str(max_val_time));
}
};
// represents a file to be stored.
// The associated EVENT is the arrival of the file
//
struct DFILE : EVENT {
META_CHUNK* meta_chunk;
double size;
int id;
set<HOST*> unused_hosts;
// hosts that don't have any chunks of this file
int pending_init_downloads;
// # of initial downloads pending.
// When this is zero, we start collecting stats for the file
double accounting_start_time;
STATS_ITEM disk_usage;
STATS_ITEM upload_rate;
STATS_ITEM download_rate;
STATS_ITEM fault_tolerance;
DFILE(double s) {
id = next_file_id++;
unused_hosts = hosts;
size = s;
}
// the creation of a file
//
virtual void handle() {
meta_chunk = new META_CHUNK(this, NULL, size, ENCODING_LEVELS, id);
#ifdef EVENT_DEBUG
printf("created file %d: size %f encoded size %f\n",
id, size, disk_usage.value
);
#endif
meta_chunk->recovery_plan();
meta_chunk->recovery_action();
}
inline bool collecting_stats() {
return (pending_init_downloads == 0);
}
void recover() {
meta_chunk->recovery_plan();
meta_chunk->recovery_action();
fault_tolerance.sample(meta_chunk->fault_tolerance, collecting_stats());
}
void print_stats() {
printf("Statistics for file %d\n", id);
printf(" Server disk usage:\n");
disk_usage.print();
printf(" Upload rate:\n");
upload_rate.print();
printf(" Download rate:\n");
download_rate.print();
printf(" Fault tolerance level:\n");
fault_tolerance.print();
}
};
//////////////////// method defs ////////////////////
// transfer has finished
//
void CHUNK_ON_HOST::handle() {
transfer_in_progress = false;
if (present_on_host) {
// it was an upload
#ifdef EVENT_DEBUG
printf("%s: upload of %s completed\n", now_str(), name);
#endif
chunk->upload_complete(); // create new replicas if needed
} else {
present_on_host = true;
#ifdef EVENT_DEBUG
printf("%s: download of %s completed\n", now_str(), name);
#endif
chunk->download_complete();
}
}
// the host has failed
//
void HOST::handle() {
set<HOST*>::iterator i = hosts.find(this);
hosts.erase(i);
#ifdef EVENT_DEBUG
printf("%s: host %d failed\n", now_str(), id);
#endif
set<CHUNK_ON_HOST*>::iterator p;
for (p = chunks.begin(); p != chunks.end(); p++) {
CHUNK_ON_HOST* c = *p;
c->chunk->host_failed(c);
if (c->transfer_in_progress) {
sim.remove(c);
}
delete c;
}
}
CHUNK::CHUNK(META_CHUNK* mc, double s, int index) {
parent = mc;
present_on_server = true;
size = s;
sprintf(name, "%s.%d", parent->name, index);
parent->dfile->pending_init_downloads += REPLICATION_LEVEL;
parent->dfile->disk_usage.sample_inc(size, false);
}
// if there aren't enough replicas of this chunk,
// pick new hosts and start downloads
//
void CHUNK::assign() {
if (!present_on_server) return;
while (hosts.size() < REPLICATION_LEVEL) {
if (parent->dfile->unused_hosts.size() == 0) {
die("no more hosts!\n");
}
set<HOST*>::iterator i = parent->dfile->unused_hosts.begin();
HOST* h = *i;
parent->dfile->unused_hosts.erase(i);
CHUNK_ON_HOST *c = new CHUNK_ON_HOST();
sprintf(c->name, "chunk %s on host %d", name, h->id);
#ifdef EVENT_DEBUG
printf("%s: assigning chunk %s to host %d\n", now_str(), name, h->id);
#endif
c->host = h;
c->chunk = this;
c->t = sim.now + (drand()+.5)*size/DOWNLOAD_BYTES_SEC;
hosts.insert(c);
parent->dfile->download_rate.sample_inc(
DOWNLOAD_BYTES_SEC,
parent->dfile->collecting_stats()
);
h->chunks.insert(c);
c->transfer_in_progress = true;
sim.insert(c);
}
}
bool CHUNK::download_in_progress() {
set<CHUNK_ON_HOST*>::iterator i;
for (i=hosts.begin(); i!=hosts.end(); i++) {
CHUNK_ON_HOST* c = *i;
if (c->download_in_progress()) return true;
}
return false;
}
void CHUNK::start_upload() {
// if no upload of this chunk is in progress, start one.
// NOTE: all instances are inherently present_on_host,
// since this is only called if chunk is not present on server
//
CHUNK_ON_HOST* c;
set<CHUNK_ON_HOST*>::iterator i;
for (i=hosts.begin(); i!=hosts.end(); i++) {
c = *i;
if (c->transfer_in_progress) return;
}
c = *(hosts.begin());
c->transfer_in_progress = true;
c->t = sim.now + (drand()+.5)*size/UPLOAD_BYTES_SEC;
parent->dfile->upload_rate.sample_inc(
UPLOAD_BYTES_SEC,
parent->dfile->collecting_stats()
);
#ifdef EVENT_DEBUG
printf("%s: starting upload of %s\n", now_str(), c->name);
#endif
sim.insert(c);
}
void CHUNK::host_failed(CHUNK_ON_HOST* p) {
set<CHUNK_ON_HOST*>::iterator i = hosts.find(p);
hosts.erase(i);
#ifdef EVENT_DEBUG
printf("%s: handling loss of %s\n", now_str(), p->name);
#endif
parent->dfile->recover();
}
void CHUNK::upload_complete() {
if (!present_on_server) {
present_on_server = true;
parent->dfile->disk_usage.sample_inc(
size,
parent->dfile->collecting_stats()
);
}
parent->dfile->recover();
parent->dfile->upload_rate.sample_inc(
-UPLOAD_BYTES_SEC,
parent->dfile->collecting_stats()
);
}
void CHUNK::download_complete() {
if (parent->dfile->pending_init_downloads) {
parent->dfile->pending_init_downloads--;
}
parent->dfile->recover();
parent->dfile->download_rate.sample_inc(
-DOWNLOAD_BYTES_SEC,
parent->dfile->collecting_stats()
);
}
META_CHUNK::META_CHUNK(
DFILE* d, META_CHUNK* par, double size, int encoding_level, int index
) {
dfile = d;
parent = par;
if (parent) {
sprintf(name, "%s.%d", parent->name, index);
} else {
sprintf(name, "%d", index);
}
if (encoding_level) {
for (int j=0; j<ENCODING_M; j++) {
children.push_back(new META_CHUNK(
d,
this,
size/ENCODING_N,
encoding_level-1,
j
));
}
} else {
for (int j=0; j<ENCODING_M; j++) {
children.push_back(new CHUNK(this, size/ENCODING_N, j));
}
}
}
// sort by increasing cost
//
bool compare_cost(const DATA_UNIT* d1, const DATA_UNIT* d2) {
return d1->cost < d2->cost;
}
// sort by decreasing fault tolerance
//
bool compare_fault_tolerance(const DATA_UNIT* d1, const DATA_UNIT* d2) {
return d1->fault_tolerance > d2->fault_tolerance;
}
// Recovery logic: decide what to do in response to
// host failures and upload/download completions.
//
// One way to do this would be to store a bunch of state info
// with each node in the file's tree,
// and do things by local tree traversal.
//
// However, it's a lot simpler (for me, the programmer)
// to store minimal state info,
// and to reconstruct state info using
// a top-down tree traversal in response to each event.
// Actually we do 2 traversals:
// 1) plan phase:
// We see whether every node recoverable,
// and if so compute its "recovery set":
// the set of children from which it can be recovered
// with minimal cost (i.e. network traffic).
// Decide whether each chunk currently on the server needs to remain.
// 2) action phase
// Based on the results of phase 1,
// decide whether to start upload/download of chunks,
// and whether to delete data currently on server
//
void META_CHUNK::recovery_plan() {
vector<DATA_UNIT*> recoverable;
vector<DATA_UNIT*> present;
unsigned int i;
have_unrecoverable_children = false;
// make lists of children in various states
//
for (i=0; i<children.size(); i++) {
DATA_UNIT* c = children[i];
c->in_recovery_set = false;
c->data_needed = false;
c->data_now_present = false;
c->recovery_plan();
switch (c->status) {
case PRESENT:
present.push_back(c);
break;
case RECOVERABLE:
recoverable.push_back(c);
break;
case UNRECOVERABLE:
have_unrecoverable_children = true;
break;
}
}
// based on states of children, decide what state we're in
//
if (present.size() >= ENCODING_N) {
status = PRESENT;
sort(present.begin(), present.end(), compare_cost);
present.resize(ENCODING_N);
cost = 0;
fault_tolerance = INT_MAX;
for (i=0; i<present.size(); i++) {
DATA_UNIT* c= present[i];
cost += c->cost;
c->in_recovery_set = true;
}
} else if (present.size() + recoverable.size() >= ENCODING_N) {
status = RECOVERABLE;
unsigned int j = ENCODING_N - present.size();
sort(recoverable.begin(), recoverable.end(), compare_cost);
cost = 0;
for (i=0; i<present.size(); i++) {
DATA_UNIT* c= present[i];
c->in_recovery_set = true;
}
for (i=0; i<j; i++) {
DATA_UNIT* c= recoverable[i];
c->in_recovery_set = true;
cost += c->cost;
}
// compute our fault tolerance
//
sort(recoverable.begin(), recoverable.end(), compare_fault_tolerance);
fault_tolerance = 0;
for (i=0; i<j; i++) {
DATA_UNIT* c= recoverable[i];
fault_tolerance += c->fault_tolerance;
}
} else {
status = UNRECOVERABLE;
}
}
const char* status_str(int status) {
switch (status) {
case PRESENT: return "present";
case RECOVERABLE: return "recoverable";
case UNRECOVERABLE: return "unrecoverable";
}
return "unknown";
}
void CHUNK::recovery_plan() {
if (present_on_server) {
status = PRESENT;
cost = 0;
fault_tolerance = INT_MAX;
} else if (hosts.size() > 0) {
status = RECOVERABLE;
cost = size;
if (hosts.size() < REPLICATION_LEVEL) {
data_needed = true;
}
fault_tolerance = hosts.size();
} else {
status = UNRECOVERABLE;
fault_tolerance = 0;
}
#ifdef DEBUG_RECOVERY
printf("chunk plan %s: status %s\n", name, status_str(status));
#endif
}
void META_CHUNK::recovery_action() {
if (data_now_present) {
status = PRESENT;
}
#ifdef DEBUG_RECOVERY
printf("meta chunk action %s state %s unrec children %d\n",
name, status_str(status), have_unrecoverable_children
);
#endif
for (unsigned i=0; i<children.size(); i++) {
DATA_UNIT* c = children[i];
#ifdef DEBUG_RECOVERY
printf(" child %s status %s in rec set %d\n",
c->name, status_str(c->status), c->in_recovery_set
);
#endif
switch (status) {
case PRESENT:
if (c->status == UNRECOVERABLE) {
c->data_now_present = true;
}
break;
case RECOVERABLE:
if (c->in_recovery_set && have_unrecoverable_children) {
c->data_needed = true;
}
break;
case UNRECOVERABLE:
break;
}
c->recovery_action();
}
}
void CHUNK::recovery_action() {
if (data_now_present) {
present_on_server = true;
parent->dfile->disk_usage.sample_inc(
size,
parent->dfile->collecting_stats()
);
status = PRESENT;
}
if (status == PRESENT && hosts.size() < REPLICATION_LEVEL) {
assign();
}
if (download_in_progress()) {
data_needed = true;
}
#ifdef DEBUG_RECOVERY
printf("chunk action: %s data_needed %d present_on_server %d\n",
name, data_needed, present_on_server
);
#endif
if (data_needed) {
if (!present_on_server) {
start_upload();
}
} else {
if (present_on_server) {
present_on_server = false;
#ifdef EVENT_DEBUG
printf("%s: %s replicated, removing from server\n", now_str(), name);
#endif
parent->dfile->disk_usage.sample_inc(
-size,
parent->dfile->collecting_stats()
);
}
}
}
set<DFILE*> dfiles;
int main() {
#if 0
HOST_ARRIVAL *h = new HOST_ARRIVAL;
h->t = 0;
sim.insert(h);
#endif
for (int i=0; i<500; i++) {
sim.insert(new HOST);
}
DFILE* dfile = new DFILE(1e2);
sim.insert(dfile);
sim.simulate(200*86400);
printf("%s: simulation finished\n", now_str());
dfile->print_stats();
}
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