1. 02 Nov, 2015 1 commit
  2. 02 Oct, 2015 9 commits
  3. 30 Sep, 2015 1 commit
    • Kirill Smelkov's avatar
      bigfile/zodb: Teach ZBlk1 not to waste memory on memory-page -> DB path · 1bf0cf31
      Kirill Smelkov authored
      ZBlk* objects are intermediate ZODB object in between data stored in
      ZODB and memory pages managed by virtmem. As such, after they do their
      job to either load data from DB to memory, or store from memory to DB,
      it is not needed to keep them alive with duplicate content thus only
      wasting memory.
      
      ZBlk0 cares about this detail via "deactivating" ._v_blkdata in
      loadblkdata() and __getstate__() prologues.
      
      ZBlk1 did the same for load path in loadblkdata() prologue, but for
      .__getstate__() it was not directly possible, because for ZBlk1 the
      state is IOBTree, not one non-persistent object, and thus it first needs
      to be processed by ZODB together with its subobjects on its way to
      storage and only then all they deactivated.
      
      So 13c0c17c (bigfile/zodb: Format #1 which is optimized for small
      changes) only put TODO for memory-page -> DB path about not wasting
      memory this way.
      
      But the problem is relatively easy to solve:
      
          - we can deactivate ZData objects (leaf objects in ZBlk1.chunktab
            btree) by hooking into ZData.__getstate__() prologue;
      
          - we also need to care to deactivate chunks right away, which
            setblkdata() loaded to compare .data and found them to be not
            changed
      
      This way we do not waste memory keeping intermediate ZData objects alive
      with the same content as memory page after commit.
      
      /cc @Tyagov
      1bf0cf31
  4. 28 Sep, 2015 5 commits
  5. 24 Sep, 2015 9 commits
    • Kirill Smelkov's avatar
      bigfile/zodb: Format #1 which is optimized for small changes · 13c0c17c
      Kirill Smelkov authored
      Our current approach is that each file block is represented by 1 zodb
      object, with block size being 2M. Even with trailing \0 trimming, which
      halves the overhead on average, DB size grows very fast if we do a lot
      of small appends or changes. So another format needs to be introduced
      which has lower overhead for storing small changes:
      
      In general, to represent BigFile as ZODB objects, each file block could
      be represented separately either as
      
          1) one ZODB object, or          (ZBlk0 - this what we have already)
          2) group of ZODB objects        (ZBlk1 - this is what we introduce)
      
      with top-level BTree directory #blk -> objects representing block.
      
      For "1" we have
      
          - low-overhead access time (only 1 object loaded from DB), but
          - high-overhead in terms of ZODB size (with FileStorage / ZEO, every change
            to a block causes it to be written into DB in full again)
      
      For "2" we have
      
          - low-overhead in terms of ZODB size (only part of a block is overwritten
            in DB on single change), but
          - high-overhead in terms of access time
            (several objects need to be loaded for 1 block)
      
      In general it is not possible to have low-overhead for both i) access-time, and
      ii) DB size, with approach where we do block objects representation /
      management on *client* side.
      
      On the other hand, if object management is moved to DB *server* side, it is
      possible to deduplicate them there and this way have low-overhead for both
      access-time and DB size with just client storing 1 object per file block. This
      will be our future approach after we teach NEO about object deduplication.
      
      ~~~~
      
      As shown above in the last paragraph it is not possible to perform
      optimally on client side. Thus ZBlk1 should be only an intermediate
      solution until we move data management to DB server side, with main
      criteria for ZBlk1 to keep it simple.
      
      In this patch a simple scheme is used, where every block is divided into
      chunks organized via BTree. When a block part changes, only corresponding
      chunk is updated. Chunk size is chosen to be 4K which creates ~ 512
      fanout for 2M block.
      
      DB size after tests is changed as follows:
      
              bigfile     bigarray
      
      ZBlk0     24K       6200K
      ZBlk1     36K         36K
      
      ( slight size increase for bigfile tests is because of btree structures
        overhead )
      
      Time to run tests stays approximately the same.
      
      /cc @Tyagov, @klaus
      13c0c17c
    • Kirill Smelkov's avatar
      bigfile/zodb: Prepare to have several ZBlk formats · 70ea8573
      Kirill Smelkov authored
      - current ZBlk becomes format 0
      - write format can be selected via WENDELIN_CORE_ZBLK_FMT env var
      - upon writing a block we always make sure we write it in current write
        format - so if a block was previously written in one format, it could
        be changed on the next write.
      - tox is prepared to test all write formats (so far only ZBlk0 there).
      
      The reason is - in the next patch we'll introduce another format for
      blocks which is optimized for small changes.
      70ea8573
    • Kirill Smelkov's avatar
      bigfile/zodb: Split common functionality from ZBlk to base class · a7b7c294
      Kirill Smelkov authored
      If we aim to have several kinds of ZBlk, the functionality to invalidate
      a block and bind it to zfile is common and thus should be shared.
      
      If we introduce a base class, it also makes sense to document what
      .loadblkdata() and .setblkdata() should do there - in one place.
      a7b7c294
    • Kirill Smelkov's avatar
      bigfile/zodb: Reuse __setstate__() in ZBlk.__init__() · a354d36b
      Kirill Smelkov authored
      - we have logic to init ._v_zfile and ._v_blk there
      
      - the same for ._v_blkdata - logic to init it is there + it is better to
        set variables right from instance creation, not hoping "it will be set
        outside from master"
      
        NOTE ._v_blkdata = None means the block was not yet loaded and
        generally fits into logic how ZBlk operates and thus the change is ok.
      a354d36b
    • Kirill Smelkov's avatar
      bigfile/zodb: Do not waste DB space storing trailing zeros for a ZBlk · f696ce92
      Kirill Smelkov authored
      A lot of times data in blocks come shorter than block size and the rest
      of the memory page is zeros (because it was pre-filled zeros by OS when
      page was allocated).
      
      Do a simple heuristic and trim those trailing zeros and not store them
      into DB.
      
      With this change size of DB created by running bigfile and bigarray
      tests changes as following:
      
                  bigfile     bigarray
      
          old     145M         35M
          new      24K          6M
      
      Trimming trailing zeros is currently done with str.rstrip('\0') which
      creates a copy. When/if needed this could be optimized to work in-place.
      f696ce92
    • Kirill Smelkov's avatar
      bigfile/zodb: Make "set blkdata to be later saved to DB" explicit method of ZBlk · e0b00bda
      Kirill Smelkov authored
      - to keep things uniform with counterpart .loadblkdata()
      - so that master do not mess with ZBlk internals and works only through
        interface - this way it will be possible to use several
        kinds of ZBlk.
      e0b00bda
    • Kirill Smelkov's avatar
      bigfile/zodb: Clarify which stage .loadblkdata() and __{get,set}state__() do · a9072290
      Kirill Smelkov authored
      All those functions move data between DB and ._v_blkdata and only master
      then connects data to memory page. Make that fact explicit.
      a9072290
    • Kirill Smelkov's avatar
      bigfile/zodb: Comments for ZBigFile + LivePersistent are ok · 0d8081c4
      Kirill Smelkov authored
      Again, leftover from 4174b84a (bigfile: BigFile backend to store data in
      ZODB).
      0d8081c4
    • Kirill Smelkov's avatar
      bigfile/zodb: __getstate__() & __setstate__() are ok · 20bad3cf
      Kirill Smelkov authored
      The comment was a leftover there from 4174b84a (bigfile: BigFile backend
      to store data in ZODB).
      20bad3cf
  6. 23 Sep, 2015 2 commits
    • Kirill Smelkov's avatar
      lib/mem: Allow memcpy destination to be bigger than source · 520cbc6f
      Kirill Smelkov authored
      i.e. it is ok to copy smaller data into larger buffer.
      520cbc6f
    • Kirill Smelkov's avatar
      lib/mem: Allow memcpy & friends to work on arbitrary-length buffer · a35106c2
      Kirill Smelkov authored
      - not only multiple of 8. We can do it by using uint8 typed arrays, and
      it does not hurt performance:
      
      In [1]: from wendelin.lib.mem import bzero, memset, memcpy
      In [2]: A = bytearray(2*1024*1024)
      In [3]: B = bytearray(2*1024*1024)
      
              memcpy(B, A)    bzero(A)        memset(A, 0xff)
      
      old:    718 µs          227 µs / 1116   228 µs / 1055 (*)
      new:    718 µs          176 µs / 1080   175 µs / 1048
      
          (*) the second number comes from e.g.
      
              In [8]: timeit bzero(A)
              The slowest run took 4.63 times longer than the fastest.
              This could mean that an intermediate result is being cached
              10000 loops, best of 3: 228 µs per loop
      
              so the second number is more realistic and says performance
              stays aproximately the same and only slightly improves.
      a35106c2
  7. 21 Sep, 2015 2 commits
    • Kirill Smelkov's avatar
      bigarray: Fix __getitem__ for cases where element overlaps with edge between pages · e5b7c31b
      Kirill Smelkov authored
      When we serve indexing request, we first compute page range in backing
      file, which contains the result based on major index range, then mmap
      that file range and pick up result from there.
      
      Page range math was however not correct: e.g. for positive strides, last
      element's byte is (byte0_stop-1), NOT (byte0_stop - byte0_stride) which
      for cases where byte0_stop is just a bit after page boundary, can make a
      difference - page_max will be 1 page less what it should be and then
      whole ndarray view creation breaks:
      
          ...
          Module wendelin.bigarray, line 381, in __getitem__
            view0 = ndarray(view0_shape, self._dtype, vma0, view0_offset, view0_stridev)
        ValueError: strides is incompatible with shape of requested array and size of buffer
      
      ( because vma0 was created less in size than what is needed to create view0_shape
        shaped array starting from view0_offset in vma0. )
      
      Similar story for negative strides math - it was not correct neither.
      
      Fix it.
      
      /reported-by @Camata
      e5b7c31b
    • Kirill Smelkov's avatar
      bigarray/tests: Factor-out generic read-only BigFile_Data · 386ae339
      Kirill Smelkov authored
      We'll need this class in tests in the next patch.
      386ae339
  8. 11 Sep, 2015 1 commit
  9. 02 Sep, 2015 2 commits
  10. 19 Aug, 2015 1 commit
  11. 18 Aug, 2015 4 commits
    • Kirill Smelkov's avatar
      bigarray: Test for correctly handling conflict on array metadata · 9752178c
      Kirill Smelkov authored
      e.g. on .shape
      9752178c
    • Kirill Smelkov's avatar
      bigfile/zodb: ZBlk._p_invalidate() can be called more than once, in particular in case of conflicts · 800c14a9
      Kirill Smelkov authored
      When there is a conflict (on any object, but on ZBlk in particular) ZODB
      machinery calls its ._p_invalidate() twice:
      
        File ".../wendelin.core/bigfile/tests/test_filezodb.py", line 661, in test_bigfile_filezodb_vs_conflicts
          tm2.commit()    # this should raise ConflictError and stay at 11 state
        File ".../transaction/_manager.py", line 111, in commit
          return self.get().commit()
        File ".../transaction/_transaction.py", line 271, in commit
          self._commitResources()
        File ".../transaction/_transaction.py", line 414, in _commitResources
          self._cleanup(L)
        File ".../transaction/_transaction.py", line 426, in _cleanup
          rm.abort(self)
        File ".../ZODB/Connection.py", line 436, in abort
          self._abort()
        File ".../ZODB/Connection.py", line 479, in _abort
          self._cache.invalidate(oid)
        File ".../wendelin.core/bigfile/file_zodb.py", line 148, in _p_invalidate
          traceback.print_stack()
      
      and
      
        File ".../wendelin.core/bigfile/tests/test_filezodb.py", line 661, in test_bigfile_filezodb_vs_conflicts
          tm2.commit()    # this should raise ConflictError and stay at 11 state
        File ".../transaction/_manager.py", line 111, in commit
          return self.get().commit()
        File ".../transaction/_transaction.py", line 271, in commit
          self._commitResources()
        File ".../transaction/_transaction.py", line 416, in _commitResources
          self._synchronizers.map(lambda s: s.afterCompletion(self))
        File ".../transaction/weakset.py", line 59, in map
          f(elt)
        File ".../transaction/_transaction.py", line 416, in <lambda>
          self._synchronizers.map(lambda s: s.afterCompletion(self))
        File ".../ZODB/Connection.py", line 831, in _storage_sync
          self._flush_invalidations()
        File ".../ZODB/Connection.py", line 539, in _flush_invalidations
          self._cache.invalidate(invalidated)
        File ".../wendelin.core/bigfile/file_zodb.py", line 148, in _p_invalidate
          traceback.print_stack()
      
      i.e. first invalidation is done by commit cleanup:
      
          https://github.com/zopefoundation/transaction/blob/1.4.4/transaction/_transaction.py#L414
          https://github.com/zopefoundation/ZODB/blob/3.10/src/ZODB/Connection.py#L479
      
      and then Connection.afterCompletion() flushes invalidation again:
      
          https://github.com/zopefoundation/transaction/blob/1.4.4/transaction/_transaction.py#L416
          https://github.com/zopefoundation/ZODB/blob/3.10/src/ZODB/Connection.py#L833
          https://github.com/zopefoundation/ZODB/blob/3.10/src/ZODB/Connection.py#L539
      
      If there was no conflict - there will be no ConflictError raised and
      thus no Transaction._cleanup() done in its ._commitResources() ->
      invalidation called only once. But with ConflictError - it is twice.
      
      Adjust ZBlk._p_invalidate() not to delve into real invalidation more
      than once - else we will fail, as ZBlk._v_zfile becomes unbound after
      invalidation done the first time.
      800c14a9
    • Kirill Smelkov's avatar
      bigarray: Test for ZBigArray invalidation via usual attribute, e.g. .shape · e6bea85f
      Kirill Smelkov authored
      All is currently handled correctly, but an observation is made that upon
      such invalidation we through away ._v_fileh i.e. we through away whole
      data cache just because an array was resized.
      e6bea85f
    • Kirill Smelkov's avatar
      bigfile/zodb: Note that even LivePersistent goes to GHOST state on invalidation · 48b2bb74
      Kirill Smelkov authored
      LivePersistent can go to ghost state, because invalidation cannot be
      ignored, i.e. they indicate the object has been changed externally.
      
      This does not break our logic for ZBigFile and ZBigArray as
      invalidations can happen only at transaction boundary, so during the
      course of transaction those classes are guaranteed to stay uptodate and
      thus not loose ._v_file and ._v_fileh (which is the reason they inherit
      from LivePersistent).
      
      it is ok to loose ._v_file and ._v_fileh at transaction boundary and
      become ghost - those objects will be recreated upon going back uptodate
      and will stay alive again during the whole transaction window.
      
      We care only not to loose e.g. ._v_fileh inside transaction, because
      loosing that data manager and thus data it manages inside transaction
      can break synchronization logic and forget changed-through-mmap data.
      48b2bb74
  12. 17 Aug, 2015 3 commits
    • Kirill Smelkov's avatar
      bigfile/zodb: Fix typos · 26d5b35e
      Kirill Smelkov authored
      26d5b35e
    • Kirill Smelkov's avatar
      bigfile/zodb: Do not hold reference to ZBigFileH indefinitely in Connection.onOpenCallback · 059c71e1
      Kirill Smelkov authored
      If we do - ZBigFileH objects just don't get garbage collected, and
      sooner or later this way it leaks enough filedescriptors so that main
      zope loop breaks:
      
          Traceback (most recent call last):
            File ".../bin/runzope", line 194, in <module>
              sys.exit(Zope2.Startup.run.run())
            File ".../eggs/Zope2-2.13.22-py2.7.egg/Zope2/Startup/run.py", line 26, in run
              starter.run()
            File ".../eggs/Zope2-2.13.22-py2.7.egg/Zope2/Startup/__init__.py", line 105, in run
              Lifetime.loop()
            File ".../eggs/Zope2-2.13.22-py2.7.egg/Lifetime/__init__.py", line 43, in loop
              lifetime_loop()
            File ".../eggs/Zope2-2.13.22-py2.7.egg/Lifetime/__init__.py", line 53, in lifetime_loop
              asyncore.poll(timeout, map)
            File ".../parts/python2.7/lib/python2.7/asyncore.py", line 145, in poll
              r, w, e = select.select(r, w, e, timeout)
          ValueError: filedescriptor out of range in select()
      
          $ lsof -p <runzope-pid> |grep ramh | wc -l
          950
      
      So continuing 64d1f40b (bigfile/zodb: Monkey-patch for ZODB.Connection
      to support callback on .open()) let's change the implementation to use
      WeakSet for callbacks list.
      
      Yes, because weakref to bound methods release immediately, we give up
      flexibility to subscribe to arbitrary callbacks. If it become an issue,
      something like WeakMethod from py3 or recipes from the net how to do it
      are there.
      059c71e1
    • Kirill Smelkov's avatar
      Drop support for ZODB < 3.10 · 105ab1c7
      Kirill Smelkov authored
      ZODB 3.10.4 was released almost 4 years ago, and contains significant
      change how ghost objects coming from DB are initially setup.
      105ab1c7