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hash: reduce mutex contention using one mutex per hash table extent

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This avoids PERFORMANCE warnings when large hash tables are used on slow
CPUs or with lots of worker threads.  It also simplifies the code (no
locksets, only one object-wide mutex instead of two).

Fixed a few minor bugs along the way (e.g. we were not setting the dirty
flag on the right hash table extent when we detected hash table errors).

Simplified error handling:  IO errors on the hash table are ignored,
instead of throwing an exception into the function that tried to use the
hash table.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This commit is contained in:
Zygo Blaxell
2018-01-10 23:08:22 -05:00
parent 365a913a26
commit 4aa5978a89
2 changed files with 151 additions and 100 deletions
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28
src/bees.h
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@ -432,18 +432,24 @@ private:
uint64_t m_buckets;
uint64_t m_extents;
uint64_t m_cells;
set<uint64_t> m_buckets_dirty;
set<uint64_t> m_buckets_missing;
BeesThread m_writeback_thread;
BeesThread m_prefetch_thread;
RateLimiter m_flush_rate_limit;
mutex m_extent_mutex;
mutex m_bucket_mutex;
condition_variable m_condvar;
set<HashType> m_toxic_hashes;
BeesStringFile m_stats_file;
LockSet<uint64_t> m_extent_lock_set;
// Mutex/condvar for the writeback thread
mutex m_dirty_mutex;
condition_variable m_dirty_condvar;
// Per-extent structures
struct ExtentMetaData {
shared_ptr<mutex> m_mutex_ptr; // Access serializer
bool m_dirty = false; // Needs to be written back to disk
bool m_missing = true; // Needs to be read from disk
ExtentMetaData();
};
vector<ExtentMetaData> m_extent_metadata;
void open_file();
void writeback_loop();
@ -451,11 +457,17 @@ private:
void try_mmap_flags(int flags);
pair<Cell *, Cell *> get_cell_range(HashType hash);
pair<uint8_t *, uint8_t *> get_extent_range(HashType hash);
void fetch_missing_extent(HashType hash);
void set_extent_dirty(HashType hash);
void fetch_missing_extent_by_hash(HashType hash);
void fetch_missing_extent_by_index(uint64_t extent_index);
void set_extent_dirty_locked(uint64_t extent_index);
void flush_dirty_extents();
bool flush_dirty_extent(uint64_t extent_index);
bool is_toxic_hash(HashType h) const;
size_t hash_to_extent_index(HashType ht);
unique_lock<mutex> lock_extent_by_hash(HashType ht);
unique_lock<mutex> lock_extent_by_index(uint64_t extent_index);
BeesHashTable(const BeesHashTable &) = delete;
BeesHashTable &operator=(const BeesHashTable &) = delete;
};