* Made the garbage collector a lot faster. It no longer computes the

complete set of live and dead paths before starting the actual
  deletion, but determines liveness on demand.  I.e. for any path in
  the store, it first tries to delete all the referrers, and then the
  path itself.  This means that the collector can start deleting paths
  almost immediately.
This commit is contained in:
Eelco Dolstra 2009-11-23 16:34:24 +00:00
parent 4f7e5f5810
commit c364d5d1e3
2 changed files with 171 additions and 169 deletions

View file

@ -401,7 +401,7 @@ static void addAdditionalRoots(PathSet & roots)
if (isInStore(*i)) { if (isInStore(*i)) {
Path path = toStorePath(*i); Path path = toStorePath(*i);
if (roots.find(path) == roots.end() && store->isValidPath(path)) { if (roots.find(path) == roots.end() && store->isValidPath(path)) {
debug(format("found additional root `%1%'") % path); debug(format("got additional root `%1%'") % path);
roots.insert(path); roots.insert(path);
} }
} }
@ -442,91 +442,159 @@ Paths topoSortPaths(const PathSet & paths)
struct GCLimitReached { }; struct GCLimitReached { };
void LocalStore::gcPath(const GCOptions & options, GCResults & results, struct LocalStore::GCState
const Path & path)
{ {
results.paths.insert(path); GCOptions options;
GCResults & results;
PathSet roots;
PathSet tempRoots;
PathSet deleted;
PathSet live;
PathSet busy;
bool gcKeepOutputs;
bool gcKeepDerivations;
GCState(GCResults & results_) : results(results_)
{
}
};
if (!pathExists(path)) return;
/* Okay, it's safe to delete. */
unsigned long long bytesFreed, blocksFreed;
deleteFromStore(path, bytesFreed, blocksFreed);
results.bytesFreed += bytesFreed;
results.blocksFreed += blocksFreed;
if (options.maxFreed && results.bytesFreed > options.maxFreed) { static bool doDelete(GCOptions::GCAction action)
printMsg(lvlInfo, format("deleted more than %1% bytes; stopping") % options.maxFreed); {
throw GCLimitReached(); return action == GCOptions::gcDeleteDead
|| action == GCOptions::gcDeleteSpecific;
}
bool LocalStore::isActiveTempFile(const GCState & state,
const Path & path, const string & suffix)
{
return hasSuffix(path, suffix)
&& state.tempRoots.find(string(path, 0, path.size() - suffix.size())) != state.tempRoots.end();
}
bool LocalStore::tryToDelete(GCState & state, const Path & path)
{
if (!pathExists(path)) return true;
if (state.deleted.find(path) != state.deleted.end()) return true;
if (state.live.find(path) != state.live.end()) return false;
startNest(nest, lvlDebug, format("considering whether to delete `%1%'") % path);
if (state.roots.find(path) != state.roots.end()) {
printMsg(lvlDebug, format("cannot delete `%1%' because it's a root") % path);
goto isLive;
} }
if (options.maxLinks) { if (isValidPath(path)) {
struct stat st;
if (stat(nixStore.c_str(), &st) == -1) /* Recursively try to delete the referrers of this path. If
throw SysError(format("statting `%1%'") % nixStore); any referrer can't be deleted, then this path can't be
if (st.st_nlink < options.maxLinks) { deleted either. */
printMsg(lvlInfo, format("link count on the store has dropped below %1%; stopping") % options.maxLinks); PathSet referrers;
throw GCLimitReached(); queryReferrers(path, referrers);
foreach (PathSet::iterator, i, referrers)
if (*i != path && !tryToDelete(state, *i)) {
printMsg(lvlDebug, format("cannot delete `%1%' because it has live referrers") % path);
goto isLive;
}
/* If gc-keep-derivations is set and this is a derivation,
then don't delete the derivation if any of the outputs are
live. */
if (state.gcKeepDerivations && isDerivation(path)) {
Derivation drv = derivationFromPath(path);
foreach (DerivationOutputs::iterator, i, drv.outputs)
if (!tryToDelete(state, i->second.path)) {
printMsg(lvlDebug, format("cannot delete derivation `%1%' because its output is alive") % path);
goto isLive;
}
}
/* If gc-keep-outputs is set, then don't delete this path if
its deriver is not garbage. !!! This is somewhat buggy,
since there might be multiple derivers, but the database
only stores one. */
if (state.gcKeepOutputs) {
Path deriver = queryDeriver(path);
/* Break an infinite recursion if gc-keep-derivations and
gc-keep-outputs are both set by tentatively assuming
that this path is garbage. This is a safe assumption
because at this point, the only thing that can prevent
it from being garbage is the deriver. Since
tryToDelete() works "upwards" through the dependency
graph, it won't encouter this path except in the call
to tryToDelete() in the gc-keep-derivation branch. */
state.deleted.insert(path);
if (deriver != "" && !tryToDelete(state, deriver)) {
state.deleted.erase(path);
printMsg(lvlDebug, format("cannot delete `%1%' because its deriver is alive") % path);
goto isLive;
}
} }
} }
}
else {
void LocalStore::gcPathRecursive(const GCOptions & options, /* A lock file belonging to a path that we're building right
GCResults & results, PathSet & done, const Path & path) now isn't garbage. */
{ if (isActiveTempFile(state, path, ".lock")) return false;
if (done.find(path) != done.end()) return;
done.insert(path);
startNest(nest, lvlDebug, format("looking at `%1%'") % path); /* Don't delete .chroot directories for derivations that are
currently being built. */
if (isActiveTempFile(state, path, ".chroot")) return false;
}
/* The path is garbage, so delete it. */
if (doDelete(state.options.action)) {
printMsg(lvlInfo, format("deleting `%1%'") % path);
unsigned long long bytesFreed, blocksFreed;
deleteFromStore(path, bytesFreed, blocksFreed);
state.results.bytesFreed += bytesFreed;
state.results.blocksFreed += blocksFreed;
if (state.options.maxFreed && state.results.bytesFreed > state.options.maxFreed) {
printMsg(lvlInfo, format("deleted more than %1% bytes; stopping") % state.options.maxFreed);
throw GCLimitReached();
}
if (state.options.maxLinks) {
struct stat st;
if (stat(nixStore.c_str(), &st) == -1)
throw SysError(format("statting `%1%'") % nixStore);
if (st.st_nlink < state.options.maxLinks) {
printMsg(lvlInfo, format("link count on the store has dropped below %1%; stopping") % state.options.maxLinks);
throw GCLimitReached();
}
}
/* Delete all the referrers first. They must be garbage too, } else
since if they were live, then the current path would also be printMsg(lvlTalkative, format("would delete `%1%'") % path);
live. Note that deleteFromStore() below still makes sure that
the referrer set has become empty, just in case. (However that state.deleted.insert(path);
doesn't guard against deleting top-level paths that are only if (state.options.action != GCOptions::gcReturnLive)
reachable from GC roots.) */ state.results.paths.insert(path);
PathSet referrers; return true;
if (isValidPath(path))
queryReferrers(path, referrers);
foreach (PathSet::iterator, i, referrers)
if (*i != path) gcPathRecursive(options, results, done, *i);
printMsg(lvlInfo, format("deleting `%1%'") % path);
gcPath(options, results, path);
}
static bool isLive(const Path & path, const PathSet & livePaths,
const PathSet & tempRoots, const PathSet & tempRootsClosed)
{
if (livePaths.find(path) != livePaths.end() ||
tempRootsClosed.find(path) != tempRootsClosed.end()) return true;
/* A lock file belonging to a path that we're building right
now isn't garbage. */
if (hasSuffix(path, ".lock") && tempRoots.find(string(path, 0, path.size() - 5)) != tempRoots.end())
return true;
/* Don't delete .chroot directories for derivations that are
currently being built. */
if (hasSuffix(path, ".chroot") && tempRoots.find(string(path, 0, path.size() - 7)) != tempRoots.end())
return true;
isLive:
state.live.insert(path);
if (state.options.action == GCOptions::gcReturnLive)
state.results.paths.insert(path);
return false; return false;
} }
void LocalStore::collectGarbage(const GCOptions & options, GCResults & results) void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
{ {
bool gcKeepOutputs = GCState state(results);
queryBoolSetting("gc-keep-outputs", false); state.options = options;
bool gcKeepDerivations =
queryBoolSetting("gc-keep-derivations", true); state.gcKeepOutputs = queryBoolSetting("gc-keep-outputs", false);
int gcKeepOutputsThreshold = state.gcKeepDerivations = queryBoolSetting("gc-keep-derivations", true);
queryIntSetting ("gc-keep-outputs-threshold", defaultGcLevel);
/* Acquire the global GC root. This prevents /* Acquire the global GC root. This prevents
a) New roots from being added. a) New roots from being added.
b) Processes from creating new temporary root files. */ b) Processes from creating new temporary root files. */
@ -537,125 +605,58 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
printMsg(lvlError, format("finding garbage collector roots...")); printMsg(lvlError, format("finding garbage collector roots..."));
Roots rootMap = options.ignoreLiveness ? Roots() : nix::findRoots(true); Roots rootMap = options.ignoreLiveness ? Roots() : nix::findRoots(true);
PathSet roots; foreach (Roots::iterator, i, rootMap) state.roots.insert(i->second);
foreach (Roots::iterator, i, rootMap) roots.insert(i->second);
/* Add additional roots returned by the program specified by the /* Add additional roots returned by the program specified by the
NIX_ROOT_FINDER environment variable. This is typically used NIX_ROOT_FINDER environment variable. This is typically used
to add running programs to the set of roots (to prevent them to add running programs to the set of roots (to prevent them
from being garbage collected). */ from being garbage collected). */
if (!options.ignoreLiveness) if (!options.ignoreLiveness)
addAdditionalRoots(roots); addAdditionalRoots(state.roots);
if (options.action == GCOptions::gcReturnRoots) { if (options.action == GCOptions::gcReturnRoots) {
results.paths = roots; results.paths = state.roots;
return;
}
/* Determine the live paths which is just the closure of the
roots under the `references' relation. */
printMsg(lvlError, format("computing live paths..."));
PathSet livePaths;
foreach (PathSet::const_iterator, i, roots)
computeFSClosure(canonPath(*i), livePaths);
if (gcKeepDerivations) {
foreach (PathSet::iterator, i, livePaths) {
/* Note that the deriver need not be valid (e.g., if we
previously ran the collector with `gcKeepDerivations'
turned off). */
Path deriver = queryDeriver(*i);
if (deriver != "" && isValidPath(deriver))
computeFSClosure(deriver, livePaths);
}
}
if (gcKeepOutputs) {
/* Hmz, identical to storePathRequisites in nix-store. */
foreach (PathSet::iterator, i, livePaths)
if (isDerivation(*i)) {
Derivation drv = derivationFromPath(*i);
string gcLevelStr = drv.env["__gcLevel"];
int gcLevel;
if (!string2Int(gcLevelStr, gcLevel))
gcLevel = defaultGcLevel;
if (gcLevel >= gcKeepOutputsThreshold)
foreach (DerivationOutputs::iterator, j, drv.outputs)
if (isValidPath(j->second.path))
computeFSClosure(j->second.path, livePaths);
}
}
if (options.action == GCOptions::gcReturnLive) {
results.paths = livePaths;
return; return;
} }
/* Read the temporary roots. This acquires read locks on all /* Read the temporary roots. This acquires read locks on all
per-process temporary root files. So after this point no paths per-process temporary root files. So after this point no paths
can be added to the set of temporary roots. */ can be added to the set of temporary roots. */
PathSet tempRoots;
FDs fds; FDs fds;
readTempRoots(tempRoots, fds); readTempRoots(state.tempRoots, fds);
state.roots.insert(state.tempRoots.begin(), state.tempRoots.end());
/* Close the temporary roots. Note that we *cannot* do this in
readTempRoots(), because there we may not have all locks yet,
meaning that an invalid path can become valid (and thus add to
the references graph) after we have added it to the closure
(and computeFSClosure() assumes that the presence of a path
means that it has already been closed). */
PathSet tempRootsClosed;
foreach (PathSet::iterator, i, tempRoots)
if (isValidPath(*i))
computeFSClosure(*i, tempRootsClosed);
else
tempRootsClosed.insert(*i);
/* After this point the set of roots or temporary roots cannot /* After this point the set of roots or temporary roots cannot
increase, since we hold locks on everything. So everything increase, since we hold locks on everything. So everything
that is not currently in in `livePaths' or `tempRootsClosed' that is not reachable from `roots'. */
can be deleted. */
/* Now either delete all garbage paths, or just the specified
/* Read the Nix store directory to find all currently existing paths (for gcDeleteSpecific). */
paths and filter out all live paths. */
printMsg(lvlError, format("reading the Nix store...")); if (options.action == GCOptions::gcDeleteSpecific) {
PathSet storePaths;
if (options.action != GCOptions::gcDeleteSpecific) {
Paths entries = readDirectory(nixStore);
foreach (Paths::iterator, i, entries) {
Path path = canonPath(nixStore + "/" + *i);
if (!isLive(path, livePaths, tempRoots, tempRootsClosed)) storePaths.insert(path);
}
}
else {
foreach (PathSet::iterator, i, options.pathsToDelete) { foreach (PathSet::iterator, i, options.pathsToDelete) {
assertStorePath(*i); assertStorePath(*i);
storePaths.insert(*i); if (!tryToDelete(state, *i))
if (isLive(*i, livePaths, tempRoots, tempRootsClosed))
throw Error(format("cannot delete path `%1%' since it is still alive") % *i); throw Error(format("cannot delete path `%1%' since it is still alive") % *i);
} }
}
} else {
printMsg(lvlError, format("reading the Nix store..."));
Paths entries = readDirectory(nixStore);
if (options.action == GCOptions::gcReturnDead) { if (doDelete(state.options.action))
results.paths.insert(storePaths.begin(), storePaths.end()); printMsg(lvlError, format("deleting garbage..."));
return; else
} printMsg(lvlError, format("determining live/dead paths..."));
/* Delete all dead store paths (or until one of the stop try {
conditions is reached), respecting the partial ordering foreach (Paths::iterator, i, entries)
determined by the references graph. */ tryToDelete(state, canonPath(nixStore + "/" + *i));
} catch (GCLimitReached & e) {
PathSet done; }
try { }
printMsg(lvlError, format("deleting garbage..."));
foreach (PathSet::iterator, i, storePaths)
gcPathRecursive(options, results, done, *i);
} catch (GCLimitReached & e) {
}
} }

View file

@ -174,12 +174,13 @@ private:
void upgradeStore12(); void upgradeStore12();
void gcPath(const GCOptions & options, GCResults & results, struct GCState;
const Path & path);
void gcPathRecursive(const GCOptions & options,
GCResults & results, PathSet & done, const Path & path);
bool tryToDelete(GCState & state, const Path & path);
bool isActiveTempFile(const GCState & state,
const Path & path, const string & suffix);
void startSubstituter(const Path & substituter, void startSubstituter(const Path & substituter,
RunningSubstituter & runningSubstituter); RunningSubstituter & runningSubstituter);
}; };