Forward pointers implementation (#651)

* initial commit for fw pointers implementation

* Finalized implementation of forward pointers

* incorporated PR comments for fw pointers implementation

* fw pointers: chunks_ids to chunk_ids

* fix for forward pointers implementation to be robust over mongo_retry with only subset of segments written

* minor fix for initialization of ARCTIC_FORWARD_POINTERS

* added implementation of cleanup/pruning supporting forward pointers and being also backwards compatible

* updated FW pointers implementation to allow any transition from/to ENABLED/DISABLED/HYBRID per write/append/read

* added comments explaining forward pointers variables and methods

* added check for number of gathered segments when updating fw pointers, and raise operation errors upon failure

* forward pointers implementation with SHAs instead of IDs

* completed fully functional implementation of SHA based forward pointers

* pruning compatible with forward pointers enabled/disabled/hybrid

* don't strip() twice in version str

* remove unnecessary import

* set back the pruning timeout to 120

* set back the pruning timeout to 120

* added numerical value of the arctic version used to crate a version, in the version metadata

* fixed index check integration test

* fixed multiple bugs with concat_and_write, corrected the pruning and fixed multiple tests after enabling for all VersionStore tests to run in all three modes for forward pointers

* fixed all integration tests for versionstore and fixed bug with pruning with FW pointers too early, as the version is not inserted yet when pruning happens

* fixed the last two broken integration tests

* fix the cleanup logic for forward pointers to retain the chunks created in the past than 24h. Added fw pointers in multiple other tests to verify functionality

* moved back in original order the publsh_changes and prune calls

* fixed python 3 compatiblility issue with pruning

* updated changelog

* fixed Binary(b'aaa') != b'aaa' in Python 3

* fixed last remaining failed tests for python 3 related to bson.binary.Binray comparison with binary

CHANGES.md

@@ -3,6 +3,8 @@
 ### 1.73 
   * Bugfix: #658 Write/append errors for Panel objects from older pandas versions
   * Feature: #653 Add version meta-info in arctic module
+  * Feature: #663 Include arctic numerical version in the metadata of the version document
+  * Feature: #650 Implemented forward pointers for chunks in VersionStore (modes: enabled/disabled/hybrid)
 
 ### 1.72 (2018-11-06)
   * Feature: #577 Added implementation for incremental serializer for numpy records

arctic/__init__.py

@@ -2,20 +2,24 @@
 
 from .arctic import Arctic, register_library_type
 from .arctic import VERSION_STORE, TICK_STORE, CHUNK_STORE
-from .store.version_store import register_versioned_storage
+from .store.version_store import register_versioned_storage, register_version
 from .store._pandas_ndarray_store import PandasDataFrameStore, PandasSeriesStore, PandasPanelStore
 from .store._ndarray_store import NdarrayStore
 
 try:
     from pkg_resources import get_distribution
     str_version = get_distribution(__name__).version.strip()
     int_parts = tuple(int(x) for x in str_version.split('.'))
+    num_version = sum([1000 ** i * v for i, v in enumerate(reversed(int_parts))])
+    register_version(str_version, num_version)
 except Exception:
     __version__ = None
     __version_parts__ = tuple()
+    __version_numerical__ = 0
 else:
     __version__ = str_version
     __version_parts__ = int_parts
+    __version_numerical__ = num_version
 
 
 register_versioned_storage(PandasDataFrameStore)

arctic/_util.py

@@ -1,7 +1,9 @@
 import logging
+import os
 
 import numpy as np
 import pymongo
+from enum import Enum
 from pandas import DataFrame
 from pandas.util.testing import assert_frame_equal
 
@@ -15,6 +17,33 @@
 _use_new_count_api = None
 
 
+# This enum provides all the available modes of operation for Forward pointers
+class FwPointersCfg(Enum):
+    ENABLED = 0   # use only forward pointers, don't update segment parent references
+    DISABLED = 1  # operate in legacy mode, update segment parent references, don't add forward pointers
+    HYBRID = 2    # maintain both forward pointers and parent references in segments; for reads prefer fw pointers
+
+
+# The version document key used to store the ObjectIDs of segments
+FW_POINTERS_REFS_KEY = 'SEGMENT_SHAS'
+# The version document key for storing the FW pointers configuration used to create this version
+FW_POINTERS_CONFIG_KEY = 'FW_POINTERS_CONFIG'
+# This variable controls has effect in Hybrid mode, and controls whether forward and regacy pointers are cross-verified
+ARCTIC_FORWARD_POINTERS_RECONCILE = bool(os.environ.get('ARCTIC_FORWARD_POINTERS_RECONCILE'))
+try:
+    # Controls the mode of operation for FW pointers, has effect on any new versions created
+    ARCTIC_FORWARD_POINTERS_CFG = FwPointersCfg[(os.environ.get('ARCTIC_FORWARD_POINTERS_CFG',
+                                                                FwPointersCfg.DISABLED.name).upper())]
+except Exception:
+    logger.exception("Failed to configure forward pointers with configuration {}".format(
+        os.environ.get('ARCTIC_FORWARD_POINTERS_CFG')))
+    ARCTIC_FORWARD_POINTERS_CFG = FwPointersCfg.DISABLED
+
+
+def get_fwptr_config(version):
+    return FwPointersCfg[version.get(FW_POINTERS_CONFIG_KEY, FwPointersCfg.DISABLED.name)]
+
+
 def _detect_new_count_api():
     try:
         mongo_v = [int(v) for v in pymongo.version.split('.')]

arctic/exceptions.py

@@ -40,9 +40,11 @@ class DataIntegrityException(ArcticException):
     """
     pass
 
+
 class ArcticSerializationException(ArcticException):
     pass
 
+
 class ConcurrentModificationException(DataIntegrityException):
     pass
 

arctic/store/_version_store_utils.py

@@ -11,7 +11,7 @@
 from pandas.compat import pickle_compat
 from pymongo.errors import OperationFailure
 
-from arctic._util import mongo_count
+from arctic._util import mongo_count, FW_POINTERS_REFS_KEY, FW_POINTERS_CONFIG_KEY, FwPointersCfg, get_fwptr_config
 
 
 def _split_arrs(array_2d, slices):
@@ -46,15 +46,28 @@ def checksum(symbol, doc):
     return Binary(sha.digest())
 
 
-def cleanup(arctic_lib, symbol, version_ids):
-    """
-    Helper method for cleaning up chunks from a version store
-    """
-    collection = arctic_lib.get_top_level_collection()
+def get_symbol_alive_shas(symbol, versions_coll):
+    return set(Binary(x) for x in versions_coll.distinct(FW_POINTERS_REFS_KEY, {'symbol': symbol}))
+
+
+def _cleanup_fw_pointers(collection, symbol, version_ids, versions_coll, shas_to_delete, do_clean=True):
+    shas_to_delete = set(shas_to_delete) if shas_to_delete else set()
+
+    if not version_ids or not shas_to_delete:
+        return shas_to_delete
+
+    symbol_alive_shas = get_symbol_alive_shas(symbol, versions_coll)
+
+    # This is the set of shas which are not referenced by any FW pointers
+    shas_safe_to_delete = shas_to_delete - symbol_alive_shas
+
+    if do_clean and shas_safe_to_delete:
+        collection.delete_many({'symbol': symbol, 'sha': {'$in': list(shas_safe_to_delete)}})
+
+    return shas_safe_to_delete
+
 
-    # Remove any chunks which contain just the parents, at the outset
-    # We do this here, because $pullALL will make an empty array: []
-    # and the index which contains the parents field will fail the unique constraint.
+def _cleanup_parent_pointers(collection, symbol, version_ids):
     for v in version_ids:
         # Remove all documents which only contain the parent
         collection.delete_many({'symbol': symbol,
@@ -69,6 +82,56 @@ def cleanup(arctic_lib, symbol, version_ids):
     collection.delete_one({'symbol':  symbol, 'parent': []})
 
 
+def _cleanup_mixed(symbol, collection, version_ids, versions_coll):
+    # Pull the deleted version IDs from the the parents field
+    collection.update_many({'symbol': symbol, 'parent': {'$in': version_ids}}, {'$pullAll': {'parent': version_ids}})
+
+    # All-inclusive set of segments which are pointed by at least one version (SHA fw pointers)
+    symbol_alive_shas = get_symbol_alive_shas(symbol, versions_coll)
+
+    spec = {'symbol': symbol, 'parent': []}
+    if symbol_alive_shas:
+        # This query unfortunately, while it hits the index (symbol, sha) to find the documents, in order to filter
+        # the documents by "parent: []" it fetches at server side, and pollutes the cache of WiredTiger
+        # TODO: add a new index for segments collection: (symbol, sha, parent)
+        spec['sha'] = {'$nin': list(symbol_alive_shas)}
+    collection.delete_many(spec)
+
+
+def _get_symbol_pointer_cfgs(symbol, versions_coll):
+    return set(get_fwptr_config(v)
+               for v in versions_coll.find({'symbol': symbol}, projection={FW_POINTERS_CONFIG_KEY: 1}))
+
+
+def cleanup(arctic_lib, symbol, version_ids, versions_coll, shas_to_delete=None, pointers_cfgs=None):
+    """
+    Helper method for cleaning up chunks from a version store
+    """
+    pointers_cfgs = set(pointers_cfgs) if pointers_cfgs else set()
+    collection = arctic_lib.get_top_level_collection()
+    version_ids = list(version_ids)
+
+    # Iterate versions to check if they are created only with fw pointers, parent pointers (old), or mixed
+    # Keep in mind that the version is not yet inserted.
+    all_symbol_pointers_cfgs = _get_symbol_pointer_cfgs(symbol, versions_coll)
+    all_symbol_pointers_cfgs.update(pointers_cfgs)
+
+    # All the versions of the symbol have been created with old arctic or with disabled forward pointers.
+    # Preserves backwards compatibility and regression for old pointers implementation.
+    if all_symbol_pointers_cfgs == {FwPointersCfg.DISABLED} or not all_symbol_pointers_cfgs:
+        _cleanup_parent_pointers(collection, symbol, version_ids)
+        return
+
+    # All the versions of the symbol we wish to delete have been created with forward pointers
+    if FwPointersCfg.DISABLED not in all_symbol_pointers_cfgs:
+        _cleanup_fw_pointers(collection, symbol, version_ids, versions_coll,
+                             shas_to_delete=shas_to_delete, do_clean=True)
+        return
+
+    # Reaching here means the symbol has versions with mixed forward pointers and legacy/parent pointer configurations
+    _cleanup_mixed(symbol, collection, version_ids, versions_coll)
+
+
 def version_base_or_id(version):
     return version.get('base_version_id', version['_id'])