allows to run parallel pipelines in separate threads (#813)

* keeps metrics of closed data writer files

* fixes handling of multiple load storages in normalize

* separates immutable job id from actual job file name

* allows to import files into data item storage

* import parquet files into data items storage in normalize

* adds buffered writer tests

* bumps to alpha 0.4.1a1

* makes all injection contexts thread affine, except config providers

* tests running parallel pipelines in thread pool

* allows to set start method for process executor

* adds thread id to dlt log

* improves parallel run test

* fixes None in toml config writer

* adds parallel asyncio test

* updates performance docs

Author: rudolfix

dlt/common/configuration/container.py

@@ -1,5 +1,7 @@
 from contextlib import contextmanager
-from typing import Dict, Iterator, Type, TypeVar
+import re
+import threading
+from typing import ClassVar, Dict, Iterator, Tuple, Type, TypeVar
 
 from dlt.common.configuration.specs.base_configuration import ContainerInjectableContext
 from dlt.common.configuration.exceptions import (
@@ -16,20 +18,33 @@ class Container:
     Injection context is identified by its type and available via dict indexer. The common pattern is to instantiate default context value
     if it is not yet present in container.
 
+    By default, the context is thread-affine so it is visible only from the thread that originally set it. This behavior may be changed
+    in particular context type (spec).
+
     The indexer is settable and allows to explicitly set the value. This is required by for context that needs to be explicitly instantiated.
 
     The `injectable_context` allows to set a context with a `with` keyword and then restore the previous one after it gets out of scope.
 
     """
 
-    _INSTANCE: "Container" = None
+    _INSTANCE: ClassVar["Container"] = None
+    _LOCK: ClassVar[threading.Lock] = threading.Lock()
+    _MAIN_THREAD_ID: ClassVar[int] = threading.get_ident()
+    """A main thread id to which get item will fallback for contexts without default"""
 
-    contexts: Dict[Type[ContainerInjectableContext], ContainerInjectableContext]
+    thread_contexts: Dict[int, Dict[Type[ContainerInjectableContext], ContainerInjectableContext]]
+    """A thread aware mapping of injection context """
+    main_context: Dict[Type[ContainerInjectableContext], ContainerInjectableContext]
+    """Injection context for the main thread"""
 
     def __new__(cls: Type["Container"]) -> "Container":
         if not cls._INSTANCE:
             cls._INSTANCE = super().__new__(cls)
-            cls._INSTANCE.contexts = {}
+            cls._INSTANCE.thread_contexts = {}
+            cls._INSTANCE.main_context = cls._INSTANCE.thread_contexts[
+                Container._MAIN_THREAD_ID
+            ] = {}
+
         return cls._INSTANCE
 
     def __init__(self) -> None:
@@ -40,48 +55,112 @@ def __getitem__(self, spec: Type[TConfiguration]) -> TConfiguration:
         if not issubclass(spec, ContainerInjectableContext):
             raise KeyError(f"{spec.__name__} is not a context")
 
-        item = self.contexts.get(spec)
+        context, item = self._thread_getitem(spec)
         if item is None:
             if spec.can_create_default:
                 item = spec()
-                self.contexts[spec] = item
+                self._thread_setitem(context, spec, item)
                 item.add_extras()
             else:
                 raise ContextDefaultCannotBeCreated(spec)
 
-        return item  # type: ignore
+        return item  # type: ignore[return-value]
 
     def __setitem__(self, spec: Type[TConfiguration], value: TConfiguration) -> None:
         # value passed to container must be final
         value.resolve()
         # put it into context
-        self.contexts[spec] = value
+        self._thread_setitem(self._thread_context(spec), spec, value)
 
     def __delitem__(self, spec: Type[TConfiguration]) -> None:
-        del self.contexts[spec]
+        context = self._thread_context(spec)
+        self._thread_delitem(context, spec)
 
     def __contains__(self, spec: Type[TConfiguration]) -> bool:
-        return spec in self.contexts
+        context = self._thread_context(spec)
+        return spec in context
+
+    def _thread_context(
+        self, spec: Type[TConfiguration]
+    ) -> Dict[Type[ContainerInjectableContext], ContainerInjectableContext]:
+        if spec.global_affinity:
+            context = self.main_context
+        else:
+            # thread pool names used in dlt contain originating thread id. use this id over pool id
+            if m := re.match(r"dlt-pool-(\d+)-", threading.currentThread().getName()):
+                thread_id = int(m.group(1))
+            else:
+                thread_id = threading.get_ident()
+            # return main context for main thread
+            if thread_id == Container._MAIN_THREAD_ID:
+                return self.main_context
+            # we may add a new empty thread context so lock here
+            with Container._LOCK:
+                context = self.thread_contexts.get(thread_id)
+                if context is None:
+                    context = self.thread_contexts[thread_id] = {}
+        return context
+
+    def _thread_getitem(
+        self, spec: Type[TConfiguration]
+    ) -> Tuple[
+        Dict[Type[ContainerInjectableContext], ContainerInjectableContext],
+        ContainerInjectableContext,
+    ]:
+        # with Container._LOCK:
+        context = self._thread_context(spec)
+        item = context.get(spec)
+        # if item is None and not spec.thread_affinity and context is not self.main_context:
+        #     item = self.main_context.get(spec)
+        return context, item
+
+    def _thread_setitem(
+        self,
+        context: Dict[Type[ContainerInjectableContext], ContainerInjectableContext],
+        spec: Type[ContainerInjectableContext],
+        value: TConfiguration,
+    ) -> None:
+        # with Container._LOCK:
+        context[spec] = value
+        # set the global context if spec is not thread affine
+        # if not spec.thread_affinity and context is not self.main_context:
+        #     self.main_context[spec] = value
+
+    def _thread_delitem(
+        self,
+        context: Dict[Type[ContainerInjectableContext], ContainerInjectableContext],
+        spec: Type[ContainerInjectableContext],
+    ) -> None:
+        del context[spec]
 
     @contextmanager
     def injectable_context(self, config: TConfiguration) -> Iterator[TConfiguration]:
         """A context manager that will insert `config` into the container and restore the previous value when it gets out of scope."""
+        config.resolve()
         spec = type(config)
         previous_config: ContainerInjectableContext = None
-        if spec in self.contexts:
-            previous_config = self.contexts[spec]
+        context, previous_config = self._thread_getitem(spec)
+
         # set new config and yield context
+        self._thread_setitem(context, spec, config)
         try:
-            self[spec] = config
             yield config
         finally:
             # before setting the previous config for given spec, check if there was no overlapping modification
-            if self.contexts[spec] is config:
+            context, current_config = self._thread_getitem(spec)
+            if current_config is config:
                 # config is injected for spec so restore previous
                 if previous_config is None:
-                    del self.contexts[spec]
+                    self._thread_delitem(context, spec)
                 else:
-                    self.contexts[spec] = previous_config
+                    self._thread_setitem(context, spec, previous_config)
             else:
                 # value was modified in the meantime and not restored
-                raise ContainerInjectableContextMangled(spec, self.contexts[spec], config)
+                raise ContainerInjectableContextMangled(spec, context[spec], config)
+
+    @staticmethod
+    def thread_pool_prefix() -> str:
+        """Creates a container friendly pool prefix that contains starting thread id. Container implementation will automatically use it
+        for any thread-affine contexts instead of using id of the pool thread
+        """
+        return f"dlt-pool-{threading.get_ident()}-"

dlt/common/configuration/inject.py

@@ -1,5 +1,4 @@
 import inspect
-import threading
 from functools import wraps
 from typing import Callable, Dict, Type, Any, Optional, Tuple, TypeVar, overload
 from inspect import Signature, Parameter
@@ -15,7 +14,6 @@
 _ORIGINAL_ARGS = "_dlt_orig_args"
 # keep a registry of all the decorated functions
 _FUNC_SPECS: Dict[int, Type[BaseConfiguration]] = {}
-_RESOLVE_LOCK = threading.Lock()
 
 TConfiguration = TypeVar("TConfiguration", bound=BaseConfiguration)
 
@@ -146,15 +144,14 @@ def _wrap(*args: Any, **kwargs: Any) -> Any:
                     sections=curr_sections,
                     merge_style=sections_merge_style,
                 )
-                # this may be called from many threads so make sure context is not mangled
-                with _RESOLVE_LOCK:
-                    with inject_section(section_context):
-                        # print(f"RESOLVE CONF in inject: {f.__name__}: {section_context.sections} vs {sections}")
-                        config = resolve_configuration(
-                            config or SPEC(),
-                            explicit_value=bound_args.arguments,
-                            accept_partial=accept_partial,
-                        )
+                # this may be called from many threads so section_context is thread affine
+                with inject_section(section_context):
+                    # print(f"RESOLVE CONF in inject: {f.__name__}: {section_context.sections} vs {sections}")
+                    config = resolve_configuration(
+                        config or SPEC(),
+                        explicit_value=bound_args.arguments,
+                        accept_partial=accept_partial,
+                    )
             resolved_params = dict(config)
             # overwrite or add resolved params
             for p in sig.parameters.values():

dlt/common/configuration/providers/toml.py

@@ -72,10 +72,14 @@ def set_value(self, key: str, value: Any, pipeline_name: str, *sections: str) ->
                 if k not in master:
                     master[k] = tomlkit.table()
                 master = master[k]  # type: ignore
-            if isinstance(value, dict) and isinstance(master.get(key), dict):
-                update_dict_nested(master[key], value)  # type: ignore
-            else:
-                master[key] = value
+            if isinstance(value, dict):
+                # remove none values, TODO: we need recursive None removal
+                value = {k: v for k, v in value.items() if v is not None}
+                # if target is also dict then merge recursively
+                if isinstance(master.get(key), dict):
+                    update_dict_nested(master[key], value)  # type: ignore
+                    return
+            master[key] = value
 
     @property
     def supports_sections(self) -> bool:

dlt/common/configuration/specs/base_configuration.py

@@ -395,6 +395,8 @@ class ContainerInjectableContext(BaseConfiguration):
 
     can_create_default: ClassVar[bool] = True
     """If True, `Container` is allowed to create default context instance, if none exists"""
+    global_affinity: ClassVar[bool] = False
+    """If True, `Container` will create context that will be visible in any thread. If False, per thread context is created"""
 
     def add_extras(self) -> None:
         """Called right after context was added to the container. Benefits mostly the config provider injection context which adds extra providers using the initial ones."""

dlt/common/configuration/specs/config_providers_context.py

@@ -1,6 +1,7 @@
 import contextlib
 import io
-from typing import List
+from typing import ClassVar, List
+
 from dlt.common.configuration.exceptions import DuplicateConfigProviderException
 from dlt.common.configuration.providers import (
     ConfigProvider,
@@ -34,6 +35,8 @@ class ConfigProvidersConfiguration(BaseConfiguration):
 class ConfigProvidersContext(ContainerInjectableContext):
     """Injectable list of providers used by the configuration `resolve` module"""
 
+    global_affinity: ClassVar[bool] = True
+
     providers: List[ConfigProvider]
     context_provider: ConfigProvider
 

dlt/common/configuration/specs/run_configuration.py

@@ -16,9 +16,7 @@ class RunConfiguration(BaseConfiguration):
     slack_incoming_hook: Optional[TSecretStrValue] = None
     dlthub_telemetry: bool = True  # enable or disable dlthub telemetry
     dlthub_telemetry_segment_write_key: str = "a1F2gc6cNYw2plyAt02sZouZcsRjG7TD"
-    log_format: str = (
-        "{asctime}|[{levelname:<21}]|{process}|{name}|{filename}|{funcName}:{lineno}|{message}"
-    )
+    log_format: str = "{asctime}|[{levelname:<21}]|{process}|{thread}|{name}|{filename}|{funcName}:{lineno}|{message}"
     log_level: str = "WARNING"
     request_timeout: float = 60
     """Timeout for http requests"""

dlt/common/data_writers/__init__.py

@@ -1,5 +1,5 @@
-from dlt.common.data_writers.writers import DataWriter, TLoaderFileFormat
-from dlt.common.data_writers.buffered import BufferedDataWriter
+from dlt.common.data_writers.writers import DataWriter, DataWriterMetrics, TLoaderFileFormat
+from dlt.common.data_writers.buffered import BufferedDataWriter, new_file_id
 from dlt.common.data_writers.escape import (
     escape_redshift_literal,
     escape_redshift_identifier,
@@ -8,8 +8,10 @@
 
 __all__ = [
     "DataWriter",
+    "DataWriterMetrics",
     "TLoaderFileFormat",
     "BufferedDataWriter",
+    "new_file_id",
     "escape_redshift_literal",
     "escape_redshift_identifier",
     "escape_bigquery_identifier",

dlt/common/data_writers/buffered.py

@@ -1,24 +1,28 @@
 import gzip
 from typing import List, IO, Any, Optional, Type, TypeVar, Generic
 
-from dlt.common.utils import uniq_id
 from dlt.common.typing import TDataItem, TDataItems
 from dlt.common.data_writers import TLoaderFileFormat
 from dlt.common.data_writers.exceptions import (
     BufferedDataWriterClosed,
     DestinationCapabilitiesRequired,
     InvalidFileNameTemplateException,
 )
-from dlt.common.data_writers.writers import DataWriter
+from dlt.common.data_writers.writers import DataWriter, DataWriterMetrics
 from dlt.common.schema.typing import TTableSchemaColumns
 from dlt.common.configuration import with_config, known_sections, configspec
 from dlt.common.configuration.specs import BaseConfiguration
 from dlt.common.destination import DestinationCapabilitiesContext
-
+from dlt.common.utils import uniq_id
 
 TWriter = TypeVar("TWriter", bound=DataWriter)
 
 
+def new_file_id() -> str:
+    """Creates new file id which is globally unique within table_name scope"""
+    return uniq_id(5)
+
+
 class BufferedDataWriter(Generic[TWriter]):
     @configspec
     class BufferedDataWriterConfiguration(BaseConfiguration):
@@ -49,7 +53,7 @@ def __init__(
         self._caps = _caps
         # validate if template has correct placeholders
         self.file_name_template = file_name_template
-        self.closed_files: List[str] = []  # all fully processed files
+        self.closed_files: List[DataWriterMetrics] = []  # all fully processed files
         # buffered items must be less than max items in file
         self.buffer_max_items = min(buffer_max_items, file_max_items or buffer_max_items)
         self.file_max_bytes = file_max_bytes
@@ -121,10 +125,20 @@ def write_data_item(self, item: TDataItems, columns: TTableSchemaColumns) -> int
         return new_rows_count
 
     def write_empty_file(self, columns: TTableSchemaColumns) -> None:
+        """Writes empty file: only header and footer without actual items"""
         if columns is not None:
             self._current_columns = dict(columns)
         self._flush_items(allow_empty_file=True)
 
+    def import_file(self, file_path: str, metrics: DataWriterMetrics) -> None:
+        # TODO: we should separate file storage from other storages. this creates circular deps
+        from dlt.common.storages import FileStorage
+
+        self._rotate_file()
+        FileStorage.link_hard_with_fallback(file_path, self._file_name)
+        self.closed_files.append(metrics._replace(file_path=self._file_name))
+        self._file_name = None
+
     def close(self) -> None:
         self._ensure_open()
         self._flush_and_close_file()
@@ -143,7 +157,7 @@ def __exit__(self, exc_type: Type[BaseException], exc_val: BaseException, exc_tb
     def _rotate_file(self) -> None:
         self._flush_and_close_file()
         self._file_name = (
-            self.file_name_template % uniq_id(5) + "." + self._file_format_spec.file_extension
+            self.file_name_template % new_file_id() + "." + self._file_format_spec.file_extension
         )
 
     def _flush_items(self, allow_empty_file: bool = False) -> None:
@@ -171,9 +185,12 @@ def _flush_and_close_file(self) -> None:
         if self._writer:
             # write the footer of a file
             self._writer.write_footer()
-            self._file.close()
+            self._file.flush()
             # add file written to the list so we can commit all the files later
-            self.closed_files.append(self._file_name)
+            self.closed_files.append(
+                DataWriterMetrics(self._file_name, self._writer.items_count, self._file.tell())
+            )
+            self._file.close()
             self._writer = None
             self._file = None
             self._file_name = None

dlt/common/data_writers/writers.py

@@ -1,6 +1,6 @@
 import abc
 from dataclasses import dataclass
-from typing import IO, TYPE_CHECKING, Any, Dict, List, Optional, Sequence, Type, Union
+from typing import IO, TYPE_CHECKING, Any, Dict, List, Optional, Sequence, Type, NamedTuple
 
 from dlt.common import json
 from dlt.common.configuration import configspec, known_sections, with_config
@@ -23,6 +23,12 @@ class TFileFormatSpec:
     supports_compression: bool = False
 
 
+class DataWriterMetrics(NamedTuple):
+    file_path: str
+    items_count: int
+    file_size: int
+
+
 class DataWriter(abc.ABC):
     def __init__(self, f: IO[Any], caps: DestinationCapabilitiesContext = None) -> None:
         self._f = f