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Provide random access to cached NARs

Browse source 
E.g.

  $ time nix cat-store --store https://cache.nixos.org?local-nar-cache=/tmp/nars \
    /nix/store/b0w2hafndl09h64fhb86kw6bmhbmnpm1-blender-2.79/share/icons/hicolor/scalable/apps/blender.svg > /dev/null
  real    0m4.139s

  $ time nix cat-store --store https://cache.nixos.org?local-nar-cache=/tmp/nars \
    /nix/store/b0w2hafndl09h64fhb86kw6bmhbmnpm1-blender-2.79/share/icons/hicolor/scalable/apps/blender.svg > /dev/null
  real    0m0.024s

(Before, the second call took ~0.220s.)

This will use a NAR listing in
/tmp/nars/b0w2hafndl09h64fhb86kw6bmhbmnpm1.ls containing all metadata,
including the offsets of regular files inside the NAR. Thus, we don't
need to read the entire NAR. (We do read the entire listing, but
that's generally pretty small. We could use a SQLite DB by borrowing
some more code from nixos-channel-scripts/file-cache.hh.)

This is primarily useful when Hydra is serving files from an S3 binary
cache, in particular when you have giant NARs. E.g. we had some 12 GiB
NARs, so accessing individuals files was pretty slow.
This commit is contained in:
Eelco Dolstra 2017-12-07 00:50:46 +01:00
parent 338f29dbd4
commit 2df9cbeb47
5 changed files with 203 additions and 109 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

12
src/libstore/binary-cache-store.cc
View file

@ -129,10 +129,8 @@ void BinaryCacheStore::addToStore(const ValidPathInfo & info, const ref<std::str
auto narAccessor = makeNarAccessor(nar);
if (accessor_) {
accessor_->nars.emplace(info.path, narAccessor);
accessor_->addToCache(info.path, *nar);
}
if (accessor_)
accessor_->addToCache(info.path, *nar, narAccessor);
{
auto res = jsonRoot.placeholder("root");
@ -144,10 +142,8 @@ void BinaryCacheStore::addToStore(const ValidPathInfo & info, const ref<std::str
}
else {
if (accessor_) {
accessor_->nars.emplace(info.path, makeNarAccessor(nar));
accessor_->addToCache(info.path, *nar);
}
if (accessor_)
accessor_->addToCache(info.path, *nar, makeNarAccessor(nar));
}
/* Compress the NAR. */

127
src/libstore/nar-accessor.cc
View file

@ -6,6 +6,8 @@
#include <stack>
#include <algorithm>
#include <nlohmann/json.hpp>
namespace nix {
struct NarMember
@ -24,31 +26,37 @@ struct NarMember
std::map<std::string, NarMember> children;
};
struct NarIndexer : ParseSink, StringSource
struct NarAccessor : public FSAccessor
{
std::shared_ptr<const std::string> nar;
GetNarBytes getNarBytes;
NarMember root;
std::stack<NarMember*> parents;
struct NarIndexer : ParseSink, StringSource
{
NarAccessor & acc;
std::stack<NarMember *> parents;
std::string currentStart;
bool isExec = false;
NarIndexer(const std::string & nar) : StringSource(nar)
{
}
NarIndexer(NarAccessor & acc, const std::string & nar)
: StringSource(nar), acc(acc)
{ }
void createMember(const Path & path, NarMember member) {
size_t level = std::count(path.begin(), path.end(), '/');
while(parents.size() > level) {
parents.pop();
}
while (parents.size() > level) parents.pop();
if(parents.empty()) {
root = std::move(member);
parents.push(&root);
if (parents.empty()) {
acc.root = std::move(member);
parents.push(&acc.root);
} else {
if(parents.top()->type != FSAccessor::Type::tDirectory) {
throw Error(format("NAR file missing parent directory of path '%1%'") % path);
}
if (parents.top()->type != FSAccessor::Type::tDirectory)
throw Error("NAR file missing parent directory of path '%s'", path);
auto result = parents.top()->children.emplace(baseNameOf(path), std::move(member));
parents.push(&result.first->second);
}
@ -56,12 +64,12 @@ struct NarIndexer : ParseSink, StringSource
void createDirectory(const Path & path) override
{
createMember(path, {FSAccessor::Type::tDirectory, false, 0, 0 });
createMember(path, {FSAccessor::Type::tDirectory, false, 0, 0});
}
void createRegularFile(const Path & path) override
{
createMember(path, {FSAccessor::Type::tRegular, false, 0, 0 });
createMember(path, {FSAccessor::Type::tRegular, false, 0, 0});
}
void isExecutable() override
@ -91,16 +99,54 @@ struct NarIndexer : ParseSink, StringSource
createMember(path,
NarMember{FSAccessor::Type::tSymlink, false, 0, 0, target});
}
};
NarMember* find(const Path & path)
NarAccessor(ref<const std::string> nar) : nar(nar)
{
NarIndexer indexer(*this, *nar);
parseDump(indexer, indexer);
}
NarAccessor(const std::string & listing, GetNarBytes getNarBytes)
: getNarBytes(getNarBytes)
{
using json = nlohmann::json;
std::function<void(NarMember &, json &)> recurse;
recurse = [&](NarMember & member, json & v) {
std::string type = v["type"];
if (type == "directory") {
member.type = FSAccessor::Type::tDirectory;
for (auto i = v["entries"].begin(); i != v["entries"].end(); ++i) {
std::string name = i.key();
recurse(member.children[name], i.value());
}
} else if (type == "regular") {
member.type = FSAccessor::Type::tRegular;
member.size = v["size"];
member.isExecutable = v.value("executable", false);
member.start = v["narOffset"];
} else if (type == "symlink") {
member.type = FSAccessor::Type::tSymlink;
member.target = v.value("target", "");
} else return;
};
json v = json::parse(listing);
recurse(root, v);
}
NarMember * find(const Path & path)
{
Path canon = path == "" ? "" : canonPath(path);
NarMember* current = &root;
NarMember * current = &root;
auto end = path.end();
for(auto it = path.begin(); it != end; ) {
for (auto it = path.begin(); it != end; ) {
// because it != end, the remaining component is non-empty so we need
// a directory
if(current->type != FSAccessor::Type::tDirectory) return nullptr;
if (current->type != FSAccessor::Type::tDirectory) return nullptr;
// skip slash (canonPath above ensures that this is always a slash)
assert(*it == '/');
@ -109,7 +155,7 @@ struct NarIndexer : ParseSink, StringSource
// lookup current component
auto next = std::find(it, end, '/');
auto child = current->children.find(std::string(it, next));
if(child == current->children.end()) return nullptr;
if (child == current->children.end()) return nullptr;
current = &child->second;
it = next;
@ -118,28 +164,16 @@ struct NarIndexer : ParseSink, StringSource
return current;
}
NarMember& at(const Path & path) {
NarMember & get(const Path & path) {
auto result = find(path);
if(result == nullptr) {
throw Error(format("NAR file does not contain path '%1%'") % path);
}
if (result == nullptr)
throw Error("NAR file does not contain path '%1%'", path);
return *result;
}
};
struct NarAccessor : public FSAccessor
{
ref<const std::string> nar;
NarIndexer indexer;
NarAccessor(ref<const std::string> nar) : nar(nar), indexer(*nar)
{
parseDump(indexer, indexer);
}
Stat stat(const Path & path) override
{
auto i = indexer.find(path);
auto i = find(path);
if (i == nullptr)
return {FSAccessor::Type::tMissing, 0, false};
return {i->type, i->size, i->isExecutable, i->start};
@ -147,30 +181,33 @@ struct NarAccessor : public FSAccessor
StringSet readDirectory(const Path & path) override
{
auto i = indexer.at(path);
auto i = get(path);
if (i.type != FSAccessor::Type::tDirectory)
throw Error(format("path '%1%' inside NAR file is not a directory") % path);
StringSet res;
for(auto&& child : i.children) {
for (auto & child : i.children)
res.insert(child.first);
}
return res;
}
std::string readFile(const Path & path) override
{
auto i = indexer.at(path);
auto i = get(path);
if (i.type != FSAccessor::Type::tRegular)
throw Error(format("path '%1%' inside NAR file is not a regular file") % path);
if (getNarBytes) return getNarBytes(i.start, i.size);
assert(nar);
return std::string(*nar, i.start, i.size);
}
std::string readLink(const Path & path) override
{
auto i = indexer.at(path);
auto i = get(path);
if (i.type != FSAccessor::Type::tSymlink)
throw Error(format("path '%1%' inside NAR file is not a symlink") % path);
return i.target;
@ -182,6 +219,12 @@ ref<FSAccessor> makeNarAccessor(ref<const std::string> nar)
return make_ref<NarAccessor>(nar);
}
ref<FSAccessor> makeLazyNarAccessor(const std::string & listing,
GetNarBytes getNarBytes)
{
return make_ref<NarAccessor>(listing, getNarBytes);
}
void listNar(JSONPlaceholder & res, ref<FSAccessor> accessor,
const Path & path, bool recurse)
{

10
src/libstore/nar-accessor.hh
View file

@ -8,6 +8,16 @@ namespace nix {
file. */
ref<FSAccessor> makeNarAccessor(ref<const std::string> nar);
/* Create a NAR accessor from a NAR listing (in the format produced by
listNar()). The callback getNarBytes(offset, length) is used by the
readFile() method of the accessor to get the contents of files
inside the NAR. */
typedef std::function<std::string(uint64_t, uint64_t)> GetNarBytes;
ref<FSAccessor> makeLazyNarAccessor(
const std::string & listing,
GetNarBytes getNarBytes);
class JSONPlaceholder;
/* Write a JSON representation of the contents of a NAR (except file

70
src/libstore/remote-fs-accessor.cc
View file

@ -1,5 +1,10 @@
#include "remote-fs-accessor.hh"
#include "nar-accessor.hh"
#include "json.hh"
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
namespace nix {
@ -11,21 +16,31 @@ RemoteFSAccessor::RemoteFSAccessor(ref<Store> store, const Path & cacheDir)
createDirs(cacheDir);
}
Path RemoteFSAccessor::makeCacheFile(const Path & storePath)
Path RemoteFSAccessor::makeCacheFile(const Path & storePath, const std::string & ext)
{
assert(cacheDir != "");
return fmt("%s/%s.nar", cacheDir, storePathToHash(storePath));
return fmt("%s/%s.%s", cacheDir, storePathToHash(storePath), ext);
}
void RemoteFSAccessor::addToCache(const Path & storePath, const std::string & nar)
void RemoteFSAccessor::addToCache(const Path & storePath, const std::string & nar,
ref<FSAccessor> narAccessor)
{
nars.emplace(storePath, narAccessor);
if (cacheDir != "") {
try {
if (cacheDir == "") return;
std::ostringstream str;
JSONPlaceholder jsonRoot(str);
listNar(jsonRoot, narAccessor, "", true);
writeFile(makeCacheFile(storePath, "ls"), str.str());
/* FIXME: do this asynchronously. */
writeFile(makeCacheFile(storePath), nar);
writeFile(makeCacheFile(storePath, "nar"), nar);
} catch (...) {
ignoreException();
}
}
}
std::pair<ref<FSAccessor>, Path> RemoteFSAccessor::fetch(const Path & path_)
@ -42,20 +57,49 @@ std::pair<ref<FSAccessor>, Path> RemoteFSAccessor::fetch(const Path & path_)
if (i != nars.end()) return {i->second, restPath};
StringSink sink;
std::string listing;
Path cacheFile;
if (cacheDir != "" && pathExists(cacheFile = makeCacheFile(storePath, "nar"))) {
try {
if (cacheDir != "")
*sink.s = nix::readFile(makeCacheFile(storePath));
listing = nix::readFile(makeCacheFile(storePath, "ls"));
auto narAccessor = makeLazyNarAccessor(listing,
[cacheFile](uint64_t offset, uint64_t length) {
AutoCloseFD fd = open(cacheFile.c_str(), O_RDONLY | O_CLOEXEC);
if (!fd)
throw SysError("opening NAR cache file '%s'", cacheFile);
if (lseek(fd.get(), offset, SEEK_SET) != (off_t) offset)
throw SysError("seeking in '%s'", cacheFile);
std::string buf(length, 0);
readFull(fd.get(), (unsigned char *) buf.data(), length);
return buf;
});
nars.emplace(storePath, narAccessor);
return {narAccessor, restPath};
} catch (SysError &) { }
if (sink.s->empty()) {
store->narFromPath(storePath, sink);
addToCache(storePath, *sink.s);
try {
*sink.s = nix::readFile(cacheFile);
auto narAccessor = makeNarAccessor(sink.s);
nars.emplace(storePath, narAccessor);
return {narAccessor, restPath};
} catch (SysError &) { }
}
auto accessor = makeNarAccessor(sink.s);
nars.emplace(storePath, accessor);
return {accessor, restPath};
store->narFromPath(storePath, sink);
auto narAccessor = makeNarAccessor(sink.s);
addToCache(storePath, *sink.s, narAccessor);
return {narAccessor, restPath};
}
FSAccessor::Stat RemoteFSAccessor::stat(const Path & path)

5
src/libstore/remote-fs-accessor.hh
View file

@ -18,9 +18,10 @@ class RemoteFSAccessor : public FSAccessor
friend class BinaryCacheStore;
Path makeCacheFile(const Path & storePath);
Path makeCacheFile(const Path & storePath, const std::string & ext);
void addToCache(const Path & storePath, const std::string & nar);
void addToCache(const Path & storePath, const std::string & nar,
ref<FSAccessor> narAccessor);
public: