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* Garbage collector: added an option `--use-atime' to delete paths in

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order of ascending last access time.  This is useful in conjunction
  with --max-freed or --max-links to prefer deleting non-recently used
  garbage, which is good (especially in the build farm) since garbage
  may become live again.

  The code could easily be modified to accept other criteria for
  ordering garbage by changing the comparison operator used by the
  priority queue in collectGarbage().
This commit is contained in:
Eelco Dolstra 2008-09-17 10:02:55 +00:00
parent 2b2aa8a820
commit 7ab68961e4
6 changed files with 225 additions and 59 deletions
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200
src/libstore/gc.cc
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@ -5,6 +5,9 @@
#include <boost/shared_ptr.hpp>
#include <functional>
#include <queue>
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
@ -439,45 +442,54 @@ Paths topoSortPaths(const PathSet & paths)
}
static time_t lastFileAccessTime(const Path & path)
{
struct stat st;
if (lstat(path.c_str(), &st) == -1)
throw SysError(format("statting `%1%'") % path);
if (S_ISDIR(st.st_mode)) {
time_t last = 0;
Strings names = readDirectory(path);
for (Strings::iterator i = names.begin(); i != names.end(); ++i) {
time_t t = lastFileAccessTime(path + "/" + *i);
if (t > last) last = t;
}
return last;
}
else if (S_ISLNK(st.st_mode)) return 0;
else return st.st_atime;
}
struct GCLimitReached { };
void LocalStore::tryToDelete(const GCOptions & options, GCResults & results,
const PathSet & livePaths, const PathSet & tempRootsClosed, PathSet & done,
const Path & path)
PathSet & done, const Path & path)
{
if (done.find(path) != done.end()) return;
done.insert(path);
debug(format("considering deletion of `%1%'") % path);
startNest(nest, lvlDebug, format("looking at `%1%'") % path);
if (livePaths.find(path) != livePaths.end()) {
if (options.action == GCOptions::gcDeleteSpecific)
throw Error(format("cannot delete path `%1%' since it is still alive") % path);
debug(format("live path `%1%'") % path);
return;
}
if (tempRootsClosed.find(path) != tempRootsClosed.end()) {
debug(format("temporary root `%1%'") % path);
return;
}
/* Delete all the referrers first. They must be garbage too,
since if they were in the closure of some live path, then this
path would also be in the closure. Note that
deleteFromStore() below still makes sure that the referrer set
has become empty, just in case. */
PathSet referrers;
if (store->isValidPath(path))
if (isValidPath(path))
queryReferrers(path, referrers);
foreach (PathSet::iterator, i, referrers)
if (*i != path)
tryToDelete(options, results, livePaths, tempRootsClosed, done, *i);
if (*i != path) tryToDelete(options, results, done, *i);
debug(format("dead path `%1%'") % path);
results.paths.insert(path);
if (!pathExists(path)) return;
/* If just returning the set of dead paths, we also return the
space that would be freed if we deleted them. */
if (options.action == GCOptions::gcReturnDead) {
@ -505,8 +517,6 @@ void LocalStore::tryToDelete(const GCOptions & options, GCResults & results,
}
#endif
if (!pathExists(path)) return;
printMsg(lvlInfo, format("deleting `%1%'") % path);
/* Okay, it's safe to delete. */
@ -538,6 +548,35 @@ void LocalStore::tryToDelete(const GCOptions & options, GCResults & results,
}
struct CachingAtimeComparator : public std::binary_function<Path, Path, bool>
{
std::map<Path, time_t> cache;
time_t lookup(const Path & p)
{
std::map<Path, time_t>::iterator i = cache.find(p);
if (i != cache.end()) return i->second;
debug(format("computing atime of `%1%'") % p);
cache[p] = lastFileAccessTime(p);
assert(cache.find(p) != cache.end());
return cache[p];
}
bool operator () (const Path & p1, const Path & p2)
{
return lookup(p2) < lookup(p1);
}
};
string showTime(const string & format, time_t t)
{
char s[128];
strftime(s, sizeof s, format.c_str(), gmtime(&t));
return string(s);
}
void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
{
bool gcKeepOutputs =
@ -587,8 +626,8 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
/* Note that the deriver need not be valid (e.g., if we
previously ran the collector with `gcKeepDerivations'
turned off). */
Path deriver = store->queryDeriver(*i);
if (deriver != "" && store->isValidPath(deriver))
Path deriver = queryDeriver(*i);
if (deriver != "" && isValidPath(deriver))
computeFSClosure(deriver, livePaths);
}
}
@ -608,7 +647,7 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
if (gcLevel >= gcKeepOutputsThreshold)
for (DerivationOutputs::iterator j = drv.outputs.begin();
j != drv.outputs.end(); ++j)
if (store->isValidPath(j->second.path))
if (isValidPath(j->second.path))
computeFSClosure(j->second.path, livePaths);
}
}
@ -633,7 +672,7 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
means that it has already been closed). */
PathSet tempRootsClosed;
for (PathSet::iterator i = tempRoots.begin(); i != tempRoots.end(); ++i)
if (store->isValidPath(*i))
if (isValidPath(*i))
computeFSClosure(*i, tempRootsClosed);
else
tempRootsClosed.insert(*i);
@ -644,32 +683,113 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
can be deleted. */
/* Read the Nix store directory to find all currently existing
paths. */
paths and filter out all live paths. */
printMsg(lvlError, format("reading the Nix store..."));
PathSet storePaths;
if (options.action != GCOptions::gcDeleteSpecific) {
Paths entries = readDirectory(nixStore);
for (Paths::iterator i = entries.begin(); i != entries.end(); ++i)
storePaths.insert(canonPath(nixStore + "/" + *i));
} else {
foreach (PathSet::iterator, i, options.pathsToDelete) {
assertStorePath(*i);
storePaths.insert(*i);
foreach (Paths::iterator, i, entries) {
Path path = canonPath(nixStore + "/" + *i);
if (livePaths.find(path) == livePaths.end() &&
tempRootsClosed.find(path) == tempRootsClosed.end())
storePaths.insert(path);
}
}
/* Try to delete store paths in the topologically sorted order. */
printMsg(lvlError, options.action == GCOptions::gcReturnDead
? format("looking for garbage...")
: format("deleting garbage..."));
else {
foreach (PathSet::iterator, i, options.pathsToDelete) {
assertStorePath(*i);
storePaths.insert(*i);
if (livePaths.find(*i) != livePaths.end())
throw Error(format("cannot delete path `%1%' since it is still alive") % *i);
if (tempRootsClosed.find(*i) != tempRootsClosed.end())
throw Error(format("cannot delete path `%1%' since it is temporarily in use") % *i);
}
}
if (options.action == GCOptions::gcReturnDead) {
results.paths.insert(storePaths.begin(), storePaths.end());
return;
}
/* Delete all dead store paths (or until one of the stop
conditions is reached). */
PathSet done;
try {
foreach (PathSet::iterator, i, storePaths)
tryToDelete(options, results, livePaths, tempRootsClosed, done, *i);
if (!options.useAtime) {
/* Delete the paths, respecting the partial ordering
determined by the references graph. */
printMsg(lvlError, format("deleting garbage..."));
foreach (PathSet::iterator, i, storePaths)
tryToDelete(options, results, done, *i);
}
else {
/* Delete in order of ascending last access time, still
maintaining the partial ordering of the reference
graph. Note that we can't use a topological sort for
this because that takes time O(V+E), and in this case
E=O(V^2) (i.e. the graph is dense because of the edges
due to the atime ordering). So instead we put all
deletable paths in a priority queue (ordered by atime),
and after deleting a path, add additional paths that
have become deletable to the priority queue. */
CachingAtimeComparator atimeComp;
/* Create a priority queue that orders paths by ascending
atime. This is why C++ needs type inferencing... */
std::priority_queue<Path, vector<Path>, binary_function_ref_adapter<CachingAtimeComparator> > prioQueue =
std::priority_queue<Path, vector<Path>, binary_function_ref_adapter<CachingAtimeComparator> >(binary_function_ref_adapter<CachingAtimeComparator>(&atimeComp));
/* Initially put the paths that are invalid or have no
referrers into the priority queue. */
printMsg(lvlError, format("finding deletable paths..."));
foreach (PathSet::iterator, i, storePaths) {
/* We can safely delete a path if it's invalid or
it has no referrers. Note that all the invalid
paths will be deleted in the first round. */
if (isValidPath(*i)) {
if (queryReferrersNoSelf(*i).empty()) prioQueue.push(*i);
} else prioQueue.push(*i);
}
debug(format("%1% initially deletable paths") % prioQueue.size());
/* Now delete everything in the order of the priority
queue until nothing is left. */
while (!prioQueue.empty()) {
Path path = prioQueue.top(); prioQueue.pop();
printMsg(lvlTalkative, format("atime %1%: %2%") % showTime("%F %H:%M:%S", atimeComp.cache[path]) % path);
PathSet references;
if (isValidPath(path)) references = queryReferencesNoSelf(path);
tryToDelete(options, results, done, path);
/* For each reference of the current path, see if the
reference has now become deletable (i.e. is in the
set of dead paths and has no referrers left). If
so add it to the priority queue. */
foreach (PathSet::iterator, i, references) {
if (storePaths.find(*i) != storePaths.end() &&
queryReferrersNoSelf(*i).empty())
{
debug(format("path `%1%' has become deletable") % *i);
prioQueue.push(*i);
}
}
}
}
} catch (GCLimitReached & e) {
}
}
}