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Add query replayer (facebookincubator#10897)
Summary: Velox can record the query metadata (query plan and configs) during task creation and input vectors of the traced operator, see facebookincubator#10774 and facebookincubator#10815. This PR adds a query replayer, it can be used to replay a query locally using the metadata and input vectors from the production environment. It supports showing the summary of a query at present, and more traced operators' replaying supports will be added in the future. Also, this PR adds two query configs `query_trace_max_bytes` and `query_trace_task_reg_exp` to constraint the record input data size and trace tasks respectively to ensure the stability of the cluster in the prod. Part of facebookincubator#9668 Pull Request resolved: facebookincubator#10897 Reviewed By: tanjialiang Differential Revision: D62336733 Pulled By: xiaoxmeng fbshipit-source-id: d196738dfa92c29fe5de67a944f652a328903814
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@@ -9,3 +9,4 @@ Debugging Tools | |
debugging/print-expr-with-stats | ||
debugging/vector-saver | ||
debugging/metrics | ||
debugging/tracing.rst |
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======= | ||
Tracing | ||
======= | ||
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Background | ||
---------- | ||
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The query trace tool helps analyze and debug query performance and correctness | ||
issues. It helps prevent interference from the test noises in a production | ||
environment (such as storage, network etc) by allowing replay of a part of the | ||
query plan and data set in an isolated environment such as a local machine. | ||
This is useful for debugging query performance debugging as we don't have to | ||
replay the whole query in a production environment. | ||
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How Tracing Tool Works | ||
---------------------- | ||
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The tracing process consists of two phases: tracing and replaying. | ||
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**Tracing Phase** | ||
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- When the query starts, the task records the metadata including query plan fragment, | ||
query configuration, and connector properties. | ||
- During the query execution, each traced operator records the input vectors and saves | ||
in the specified storage location. | ||
- The metadata are serialized using json format and operator data inputs are serialized | ||
using `Presto serializer <https://prestodb.io/docs/current/develop/serialized-page.html>`_. | ||
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**Replaying Phase** | ||
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1. Read and deserialize the recorded query plan in tracing phase, extract the target plan | ||
node, and assemble a plan fragment with a customized source and sink nodes. The source | ||
node reads the input from the serialized operator inputs on storage and sink operator | ||
prints or logs out the execution stats. | ||
2. Build a task with the assembled plan fragment in step 1. | ||
3. Apply the recorded query configuration and connector properties to replay the task with | ||
the same input and configuration as in production. | ||
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**NOTE**: The Presto serialization doesn't always preserve vector encoding (lazy vectors are | ||
loaded, nested dictionaries are flattened). Hence, replay may differ from the original run. | ||
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.. image:: ../images/trace-arch.png | ||
:width: 600 | ||
:align: center | ||
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Tracing Framework | ||
----------------- | ||
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The tracing framework consists of three components: | ||
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1. **Metadata and Data Writer**: metadata writer and the data writer. | ||
2. **Metadata and Data Reader**: metadata reader and the data reader. | ||
3. **Query Trace Replayer**: display query summaries or replay the | ||
execution of the target operator. | ||
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Query Trace Writer | ||
^^^^^^^^^^^^^^^^^^ | ||
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**QueryMetadataWriter** records the query metadata during task creation, | ||
serializes, and writes them into a file in JSON format. There are two kinds | ||
of metadata: | ||
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- Query configurations and connector properties are specified by the user per query. | ||
They can be serialized as JSON map objects (key-value pairs). | ||
- Plan fragment of the task (also known as a plan node tree). It can be serialized | ||
as a JSON object, which is already supported in Velox. | ||
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**QueryDataWriter** records the input vectors from the target operator, which are | ||
serialized and written as a binary file. | ||
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Query Trace Reader | ||
^^^^^^^^^^^^^^^^^^ | ||
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**QueryMetadataReader** can load the query metadata JSON file, and extract the query | ||
configurations, connector properties, and the plan fragment. | ||
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**QueryDataReader** can read and deserialize the input vectors of the target operator. | ||
It is used as the utility to replay the input data as a source operator in the target | ||
operator replay. | ||
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**NOTE**: `QueryDataWriter` serializes and flushes the input vectors in batches, | ||
allowing it to replay the input process using the same sequence of batches. | ||
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Query Trace Util | ||
^^^^^^^^^^^^^^^^ | ||
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- Create tracing directories. | ||
- Get query summaries. | ||
- Provide utilities to extract the target plan node, and assemble a plan fragment with | ||
customized trace source and sink node with it. | ||
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Query Trace Tool | ||
---------------- | ||
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The query trace tool leverages the trace reader to display query summaries and replay the | ||
execution of specific operators (TBD). | ||
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Tracing tools Usage | ||
^^^^^^^^^^^^^^^^^^^ | ||
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.. code-block:: c++ | ||
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query_replayer --root $root_dir --summary --pretty | ||
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It would show something as the follows | ||
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.. code-block:: c++ | ||
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++++++Query trace summary++++++ | ||
Number of tasks: 1 | ||
Task ids: task-1 | ||
++++++Query configs and plan:++++++ | ||
{ | ||
"planNode":{ | ||
"filter":{}, | ||
"outputType":{...}, | ||
"nullAware":false, | ||
"sources":[{...}, {...}], | ||
"leftKeys":[], | ||
"joinType":"INNER", | ||
"id":"5", | ||
"name":"HashJoinNode" | ||
}, | ||
"connectorProperties":{...}, | ||
"queryConfig":{...} | ||
} | ||
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Here is a full list of supported command line arguments. | ||
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* ``--usage``: Show the usage. | ||
* ``--root``: Root dir of the query tracing. | ||
* ``--summary``: Show the summary of the tracing including number of tasks and task ids. | ||
It also print the query metadata including query configs, connectors properties, and query plan in JSON format. | ||
* ``--short_summary``: Only show number of tasks and task ids. | ||
* ``--task_id``: Specify the target task id, if empty, show the summary of all the traced query tasks. | ||
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Future Work | ||
----------- | ||
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https://github.com/facebookincubator/velox/issues/9668 |
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