lix/src/libstore/globals.cc
Eelco Dolstra 11800e6198 download-from-binary-cache: parallelise fetching of NAR info files
Getting substitute information using the binary cache substituter has
non-trivial latency overhead.  A package or NixOS system configuration
can have hundreds of dependencies, and in the worst case (when the
local info cache is empty) we have to do a separate HTTP request for
each of these.  If the ping time to the server is t, getting N info
files will take tN seconds; e.g., with a ping time of 0.1s to
nixos.org, sequentially downloading 1000 info files (a typical NixOS
config) will take at least 100 seconds.

To fix this problem, the binary cache substituter can now perform
requests in parallel.  This required changing the substituter
interface to support a function querySubstitutablePathInfos() that
queries multiple paths at the same time, and rewriting queryMissing()
to take advantage of parallelism.  (Due to local caching,
parallelising queryMissing() is sufficient for most use cases, since
it's almost always called before building a derivation and thus fills
the local info cache.)

For example, parallelism speeds up querying all 1056 paths in a
particular NixOS system configuration from 116s to 2.6s.  It works so
well because the eccentricity of the top-level derivation in the
dependency graph is only 9.  So we only need 10 round-trips (when
using an unlimited number of parallel connections) to get everything.

Currently we do a maximum of 150 parallel connections to the server.
Thus it's important that the binary cache server (e.g. nixos.org) has
a high connection limit.  Alternatively we could use HTTP pipelining,
but WWW::Curl doesn't support it and libcurl has a hard-coded limit of
5 requests per pipeline.
2012-07-06 19:08:20 -04:00

174 lines
4.6 KiB
C++

#include "config.h"
#include "globals.hh"
#include "util.hh"
#include <map>
#include <algorithm>
namespace nix {
string nixStore = "/UNINIT";
string nixDataDir = "/UNINIT";
string nixLogDir = "/UNINIT";
string nixStateDir = "/UNINIT";
string nixDBPath = "/UNINIT";
string nixConfDir = "/UNINIT";
string nixLibexecDir = "/UNINIT";
string nixBinDir = "/UNINIT";
bool keepFailed = false;
bool keepGoing = false;
bool tryFallback = false;
Verbosity buildVerbosity = lvlError;
unsigned int maxBuildJobs = 1;
unsigned int buildCores = 1;
bool readOnlyMode = false;
string thisSystem = "unset";
time_t maxSilentTime = 0;
time_t buildTimeout = 0;
Paths substituters;
bool useBuildHook = true;
bool printBuildTrace = false;
static bool settingsRead = false;
static std::map<string, Strings> settings;
/* Overriden settings. */
std::map<string, Strings> settingsCmdline;
string & at(Strings & ss, unsigned int n)
{
Strings::iterator i = ss.begin();
advance(i, n);
return *i;
}
static void readSettings()
{
Path settingsFile = (format("%1%/%2%") % nixConfDir % "nix.conf").str();
if (!pathExists(settingsFile)) return;
string contents = readFile(settingsFile);
unsigned int pos = 0;
while (pos < contents.size()) {
string line;
while (pos < contents.size() && contents[pos] != '\n')
line += contents[pos++];
pos++;
string::size_type hash = line.find('#');
if (hash != string::npos)
line = string(line, 0, hash);
Strings tokens = tokenizeString(line);
if (tokens.empty()) continue;
if (tokens.size() < 2 || at(tokens, 1) != "=")
throw Error(format("illegal configuration line `%1%' in `%2%'") % line % settingsFile);
string name = at(tokens, 0);
Strings::iterator i = tokens.begin();
advance(i, 2);
settings[name] = Strings(i, tokens.end());
};
settings.insert(settingsCmdline.begin(), settingsCmdline.end());
settingsRead = true;
}
Strings querySetting(const string & name, const Strings & def)
{
if (!settingsRead) readSettings();
std::map<string, Strings>::iterator i = settings.find(name);
return i == settings.end() ? def : i->second;
}
string querySetting(const string & name, const string & def)
{
Strings defs;
defs.push_back(def);
Strings value = querySetting(name, defs);
if (value.size() != 1)
throw Error(format("configuration option `%1%' should not be a list") % name);
return value.front();
}
bool queryBoolSetting(const string & name, bool def)
{
string v = querySetting(name, def ? "true" : "false");
if (v == "true") return true;
else if (v == "false") return false;
else throw Error(format("configuration option `%1%' should be either `true' or `false', not `%2%'")
% name % v);
}
unsigned int queryIntSetting(const string & name, unsigned int def)
{
int n;
if (!string2Int(querySetting(name, int2String(def)), n) || n < 0)
throw Error(format("configuration setting `%1%' should have an integer value") % name);
return n;
}
void overrideSetting(const string & name, const Strings & value)
{
if (settingsRead) settings[name] = value;
settingsCmdline[name] = value;
}
void reloadSettings()
{
settingsRead = false;
settings.clear();
}
void setDefaultsFromEnvironment()
{
/* Setup Nix paths. */
nixStore = canonPath(getEnv("NIX_STORE_DIR", getEnv("NIX_STORE", NIX_STORE_DIR)));
nixDataDir = canonPath(getEnv("NIX_DATA_DIR", NIX_DATA_DIR));
nixLogDir = canonPath(getEnv("NIX_LOG_DIR", NIX_LOG_DIR));
nixStateDir = canonPath(getEnv("NIX_STATE_DIR", NIX_STATE_DIR));
nixDBPath = getEnv("NIX_DB_DIR", nixStateDir + "/db");
nixConfDir = canonPath(getEnv("NIX_CONF_DIR", NIX_CONF_DIR));
nixLibexecDir = canonPath(getEnv("NIX_LIBEXEC_DIR", NIX_LIBEXEC_DIR));
nixBinDir = canonPath(getEnv("NIX_BIN_DIR", NIX_BIN_DIR));
string subs = getEnv("NIX_SUBSTITUTERS", "default");
if (subs == "default") {
//substituters.push_back(nixLibexecDir + "/nix/substituters/copy-from-other-stores.pl");
//substituters.push_back(nixLibexecDir + "/nix/substituters/download-using-manifests.pl");
substituters.push_back(nixLibexecDir + "/nix/substituters/download-from-binary-cache.pl");
} else
substituters = tokenizeString(subs, ":");
/* Get some settings from the configuration file. */
thisSystem = querySetting("system", SYSTEM);
maxBuildJobs = queryIntSetting("build-max-jobs", 1);
buildCores = queryIntSetting("build-cores", 1);
maxSilentTime = queryIntSetting("build-max-silent-time", 0);
buildTimeout = queryIntSetting("build-timeout", 0);
}
}