1. 18 Jan, 2019 5 commits
    • Kirill Smelkov's avatar
      go/zodb: Allow to set live cache control policy · cab4dd52
      Kirill Smelkov authored
      This allows for applications to tune eviction strategy for their needs.
      The interface to do so (LiveCacheControl) was defined previously in
      c67ff9ea (go/zodb: Connection: Allow applications to tune live-cache
      eviction policy), but so far there was no way to install cache
      controller. Fix it.
      cab4dd52
    • Kirill Smelkov's avatar
      go/zodb: Expose access to connection's live cache as public API · e2d902b0
      Kirill Smelkov authored
      Wendelin.core (wcfs) needs to check whether an object is currently
      cached or not.
      e2d902b0
    • Kirill Smelkov's avatar
      go/zodb/fs1: Teach it to support notifications on database change · db852511
      Kirill Smelkov authored
      Following-up on 4d2c8b1d (go/zodb: Require drivers to provide
      notifications for database change events) let's teach FileStorage to
      support watching for database changes:
      
      - add watcher who observes changes to data file via fsnotify.
      
      - when we see that the file was updated - there is a tricky case to distinguish
        in-progress writes from just some garbage added at tail. See comments in
        _watcher for details.
      
      - if the watcher sees there is indeed new transactions, the watcher
        updates index & txnh{Min,Max} and sends corresponding event to watchq.
      
      - since index / txnh{Min,Max} can now be changed (by watcher) -> they
        are now protected by mu.
      
      - consequently operations like LastTid, LastOid, Load, ... are all taught to
        observe index / txnh{Min,Max} state in read-snapshot way.
      
      - add down & friends to indicate that the storage is no longer
        operational, if watcher sees there is a problem with data file.
      
      - Open is reworked to start from loading/rebuilding index first, and then tail
        to watcher to detect whether what's after found topPos is garbage or another
        in-progress transaction. Consequently it is now possible to correctly open
        filestorage that is being currently written to and has in-progress transaction
        at tail.
      
      The patch is a bit big, but the changes here are all tightly
      interrelated.
      db852511
    • Kirill Smelkov's avatar
      go/zodb/fs1: Factor out making zodb.OpError into FileStorage.zerr · 8eb0988e
      Kirill Smelkov authored
      It is already 3 places where we return zodb.OpError and it will be more.
      Make a helper function to create those errors with higher signal/noise.
      8eb0988e
    • Kirill Smelkov's avatar
      go/zodb: Require drivers to provide notifications for database change events · 4d2c8b1d
      Kirill Smelkov authored
      A ZODB database can be changed by local client as well as another
      process. A notification channel is thus needed for local cache and
      database view to know they have to update to current database state.
      
      This patch builds the interface of how such notifications should be
      provided by drivers. Contrary to ZODB/py it is required that every
      driver provide it.
      
      However we will be providing driver support incrementally and for now
      all drivers behave as if the database is not changing.
      
      A note on why Watchq is passed to driver as options: low-level ZODB
      users, who might want to work with drivers directly, might not need it,
      and this way with Watchq not present in driver options they will continue to
      observe the same driver behaviour as before watchq was introduced. In
      practice many low-level utilities don't need notification support, and
      it would be not good to required them all to update open calls and to
      provide watchq drainer not to get stuck.
      
      TODO Watchq should be extended to also receive errors from watcher, so
      that clients could be notified when there is something wrong with the
      database.
      4d2c8b1d
  2. 17 Jan, 2019 9 commits
  3. 13 Dec, 2018 1 commit
  4. 04 Dec, 2018 1 commit
  5. 08 Oct, 2018 9 commits
  6. 02 Oct, 2018 1 commit
  7. 01 Oct, 2018 1 commit
    • Kirill Smelkov's avatar
      go/zodb: Don't truncate Tid time precision to 1µs · 9112f21e
      Kirill Smelkov authored
      The format of tid assumes ~ ns precision, and it is only formatted to µs
      precision by default. So don't truncate TimeStamp value when computing
      it from Tid, and perform the µs-rounding only on formatting.
      
      The float numbers are not always exactly as in python. For example the
      following program
      
      	tidv = [
      	    0x0000000000000000,
      	    0x0285cbac258bf266,
      	    0x0285cbad27ae14e6,
      	    0x037969f722a53488,
      	    0x03b84285d71c57dd,
      	    0x03caa84275fc1166,
      	]
      
      	for tid in tidv:
      	    t = TimeStamp.TimeStamp(p64(tid))
      	    print '0x%016x %s %.9f\t%.9f' % (tid, t, t.timeTime(), t.second())
      
      prints:
      
      	0x0000000000000000 1900-01-01 00:00:00.000000 -2208988800.000000000     0.000000000
      	0x0285cbac258bf266 1979-01-03 21:00:08.800000 284245208.800000191       8.800000185
      	0x0285cbad27ae14e6 1979-01-03 21:01:09.300001 284245269.300001621       9.300001496	<-- ex here
      	0x037969f722a53488 2008-10-24 05:11:08.120000 1224825068.119999886      8.119999878
      	0x03b84285d71c57dd 2016-07-01 09:41:50.416574 1467366110.416574001      50.416573989
      	0x03caa84275fc1166 2018-10-01 16:34:27.652650 1538411667.652649879      27.652650112
      
      the difference is due to floating point operation ordering, because
      TimeStamp.timeTime() looses precision - e.g. for marked case:
      
      	In [8]: '%.10f' % (281566860.000000000 + 9.300001496)
      	Out[8]: '281566869.3000015020'
      
      We don't try to mimic float64 behaviour to Python exactly - because it is even
      different for PURE_PYTHON=y or C TimeStamp implementations. However we don't
      limit due to that our timestamp precision to only 1µs.
      
      In other words we keep on maintaining exact compatibility with Python on
      printing, but timestamp values itself are now ~ ns precision.
      9112f21e
  8. 28 Sep, 2018 1 commit
    • Kirill Smelkov's avatar
      go/zodb/fs1/index: Don't rely on []byte being pickled as string · c72aaa0d
      Kirill Smelkov authored
      As https://github.com/kisielk/og-rek/pull/57 maybe shows []byte was
      pickling as string only unintentionally and that might change.
      
      We are already explicitly checking for string in corresponding index
      load place:
      
      	https://lab.nexedi.com/kirr/neo/blob/2dba8607/go/zodb/storage/fs1/index.go#L282
      
      so it is better we also explicitly save the bits as string.
      
      If we don't and https://github.com/kisielk/og-rek/pull/57 gets accepted,
      tests will fail:
      
      	--- FAIL: TestIndexSaveLoad (0.00s)
      	    index_test.go:176: index load: /tmp/t-index893650059/458967662/1.fs.index: pickle @6: invalid oidPrefix: type []uint8
      	Traceback (most recent call last):
      	  File "./py/indexcmp", line 41, in <module>
      	    main()
      	  File "./py/indexcmp", line 29, in main
      	    d2 = fsIndex.load(path2)
      	  File "/home/kirr/src/wendelin/z/ZODB/src/ZODB/fsIndex.py", line 138, in load
      	    data[ensure_bytes(k)] = fsBucket().fromString(ensure_bytes(v))
      	  File "/home/kirr/src/wendelin/z/ZODB/src/ZODB/fsIndex.py", line 71, in ensure_bytes
      	    return s.encode('ascii') if not isinstance(s, bytes) else s
      	AttributeError: 'bytearray' object has no attribute 'encode'
      	--- FAIL: TestIndexSaveToPy (0.04s)
      	    index_test.go:218: zodb/py read/compare index: exit status 1
      c72aaa0d
  9. 09 Aug, 2018 12 commits
    • Kirill Smelkov's avatar
      go/zodb/btree: New package to work with ZODB BTrees (draft) · 2dba8607
      Kirill Smelkov authored
      Provide minimal support for BTrees.LOBTree Get for now.
      2dba8607
    • Kirill Smelkov's avatar
      go/zodb: DB - application-level handle to database (very draft) · 533f0c73
      Kirill Smelkov authored
      DB represents a handle to database at application level and contains pool
      of connections. DB.Open opens database connection. The connection will be
      automatically put back into DB pool for future reuse after corresponding
      transaction is complete. DB thus provides service to maintain live objects
      cache and reuse live objects from transaction to transaction.
      
      Note that it is possible to have several DB handles to the same database.
      This might be useful if application accesses distinctly different sets of
      objects in different transactions and knows beforehand which set it will be
      next time. Then, to avoid huge cache misses, it makes sense to keep DB
      handles opened for every possible case of application access.
      
      TODO handle invalidations.
      533f0c73
    • Kirill Smelkov's avatar
      go/zodb: Connection: Allow applications to tune live-cache eviction policy · c67ff9ea
      Kirill Smelkov authored
      For example Wendelin.core wcfs will need to keep some types of objects
      (e.g. BigFile index) always in RAM for efficiency.
      
      Provide corresponding interface that application could use to install
      such live-cache eviction decision-making tuning.
      c67ff9ea
    • Kirill Smelkov's avatar
      go/zodb: Implement Connection · fb343a6f
      Kirill Smelkov authored
      Connection represents an application-level view of a ZODB database.
      It has groups of in-RAM application-level objects associated with it.
      The objects are isolated from both changes in further database
      transactions and from changes to in-RAM objects in other connections.
      
      Connection, as objects group manager, is responsible for handling
      object -> object database references. For this to work it keeps
      
      	{} oid -> obj
      
      dict and uses it to find already loaded object when another object
      persistently references particular oid. Since it related pydata handling
      of persistent references is correspondingly implemented in this patch.
      
      The dict must keep weak references on objects. The following text
      explains the rationale:
      
      	if Connection keeps strong link to obj, just
      	obj.PDeactivate will not fully release obj if there are no
      	references to it from other objects:
      
      	     - deactivate will release obj state (ok)
      	     - but there will be still reference from connection `oid -> obj` map to this object,
      	       which means the object won't be garbage-collected.
      
      	-> we can solve it by using "weak" pointers in the map.
      
      	NOTE we cannot use regular map and arbitrarily manually "gc" entries
      	there periodically: since for an obj we don't know whether other
      	objects are referencing it, we can't just remove obj's oid from
      	the map - if we do so and there are other live objects that
      	reference obj, user code can still reach obj via those
      	references. On the other hand, if another, not yet loaded, object
      	also references obj and gets loaded, traversing reference from
      	that loaded object will load second copy of obj, thus breaking 1
      	object in db <-> 1 live object invariant:
      
      	     A  →  B  →  C
      	     ↓           |
      	     D <--------- - - -> D2 (wrong)
      
      	- A activate
      	- D activate
      	- B activate
      	- D gc, A still keeps link on D
      	- C activate -> it needs to get to D, but D was removed from objtab
      	  -> new D2 is wrongly created
      
      	that's why we have to depend on Go's GC to know whether there are
      	still live references left or not. And that in turn means finalizers
      	and thus weak references.
      
      	some link on the subject:
      	https://groups.google.com/forum/#!topic/golang-nuts/PYWxjT2v6ps
      fb343a6f
    • Kirill Smelkov's avatar
      go/zodb/internal/weak: New package to handle weak references · 79e28f3c
      Kirill Smelkov authored
      We will need weak references to handle {} oid -> obj inside zodb.Connection .
      
      In Go world they often say that weak references are not needed at all.
      Please see however the next patch for detailed rationale for why weak
      references (finalizers and cooperation from Go's GC in other words) are
      _required_ in that case.
      79e28f3c
    • Kirill Smelkov's avatar
      go/zodb: PyStateful persistency support · 532d014f
      Kirill Smelkov authored
      As promised in 354e0e51 (go/zodb: Persistent - the base type to
      implement IPersistent objects) add support to persistency machinery to
      set object state from python pickles serialized by ZODB/py.
      
      Persistent references are not yet handled.
      
      As promised add some very minimal persistent tests.
      532d014f
    • Kirill Smelkov's avatar
      go/zodb: pydata: Factor out class extraction logic into xpyclass · abc11031
      Kirill Smelkov authored
      Currently we handle many ways ZODB could serialize a Python class in
      PyData.ClassName. Since we'll be using this functionality in other
      places soon - extract it into dedicated function.
      
      Since will be also frequently using
      
      	class.__module__ + "." + class.__name__
      
      don't inline it in ClassName and instead put it into pyclassPath() right
      away.
      abc11031
    • Kirill Smelkov's avatar
      go/zodb: Persistent - the base type to implement IPersistent objects · 354e0e51
      Kirill Smelkov authored
      Add the base type, that types which want to implement persistency
      could embed, and this way inherit persistent functionality. For example
      
      	type MyObject struct {
      		Persistent
      		...
      	}
      
      	type myObjectState MyObject
      
      	func (o *myObjectState) DropState() { ... }
      	func (o *myObjectState) SetState(state *mem.Buf) error { ... }
      
      Here state management methods (DropState and SetState) will be
      automatically used by persistency machinery on activation and
      deactivation.
      
      For this to work MyObject class has to be registered to ZODB
      
      	func init() {
      		t := reflect.TypeOf
      		zodb.RegisterClass("mymodule.MyObject", t(MyObject{}), t(myObjectState))
      	}
      
      and new instances of MyObject has to be created via zodb.NewPersistent:
      
      	obj := zodb.NewPersistent(reflect.TypeOf(MyObject{}), jar).(*MyObject)
      
      SetState corresponds to __setstate__ in Python. However in Go version it
      is explicitly separated from class's public API - as it is the contract
      between a class and persistency machinery, not between the class and its
      user. Notice that SetState takes raw buffer as its argument. In the
      following patch we'll add SetState cousing (PySetState) that will be
      taking unpickled objects as the state - exactly how __setstate__
      operates in Python. Classes will be able to choose whether to accept
      state as raw bytes or as a python object.
      
      The activation/deactivation is implemented via reference counting.
      
      Tests are pending (for PySetState).
      354e0e51
    • Kirill Smelkov's avatar
      go/zodb: IPersistent + Connection stub · f6a27a1e
      Kirill Smelkov authored
      Add to ZODB/go IPersistent - the interface that is used to represent
      in-RAM application-level objects that are mirroring objects in database.
      
      The interface is modelled after Python's IPersistent
      
      	https://github.com/zopefoundation/ZODB/blob/3.10.7-4-gb8d7a8567/src/persistent/interfaces.py#L22
      
      but is not exactly equal to it. In particular we support concurrent
      access to an object from multiple goroutines simultaneously.
      
      Due to concurrency support there is no STICKY state, because STICKY is
      used in CPython version to temporarily pin object in RAM briefly and is
      not safe to use from multiple threads there. Correspondingly the
      semantic of PActivate is a bit different from _p_activate - in Go, after
      an object has been activated, it is guaranteed that it will remain
      present in RAM until it is explicitly deactivated by user.
      
      Please see details of the activation protocol in IPersistent
      documentation.
      
      ZODB/py uses interface (IDataManager) for a persistent-object's jar, but
      in Go I decided, at least for now, to go without explicit interface at
      that level. For this reason a concrete type - Connection - will be used,
      and so its stub is also introduced in the patch, since IPersistent wants
      to return the connection via PJar.
      f6a27a1e
    • Kirill Smelkov's avatar
      go/zodb: pkgdoc: Add section overviewing storage drivers · 9b751272
      Kirill Smelkov authored
      We already have the functionality, just add an overview on how to
      implement drivers and use the most common ones.
      9b751272
    • Kirill Smelkov's avatar
      go/zodb: pkgdoc: Put zodbtools reference into "Miscellaneous" section · 498606b4
      Kirill Smelkov authored
      There will be many text added to pkgdoc with new sections and
      per-section footnotes, and this way it is better to use a dedicated
      section for references instead of global footnote whose context might
      become unclear.
      498606b4
    • Kirill Smelkov's avatar
      go/zodb: pkgdoc: "Operations" -> "Storage layer" · 25170e24
      Kirill Smelkov authored
      As we are going to add another - "Application layer" to zodb package,
      turn previous text overviewing IStorage & friends into "Storage layer"
      section.
      25170e24