Add timestamp and timezone management documentation #10036
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mbasmanova
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Jun 5, 2024
velox/docs/develop/timestamp.rst
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| reading of a wall clock and a calendar, e.g, ``2024-04-09 18:25:00``. Note that | ||
| a TIMESTAMP does not represent an absolute point in time, as the exact same | ||
| wall clock time may be read in different instants in time depending on where | ||
| one is situated on earth. For example, ``2024-04-09 18:25:00`` in California |
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nit: wondering if earth should be Earth
velox/docs/develop/timestamp.rst
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| a TIMESTAMP does not represent an absolute point in time, as the exact same | ||
| wall clock time may be read in different instants in time depending on where | ||
| one is situated on earth. For example, ``2024-04-09 18:25:00`` in California | ||
| and in China were perceived at different absolute points in time, about 15h |
velox/docs/develop/timestamp.rst
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| * While “seconds” can be negative to represent time before ``1970-01-01 | ||
| 00:00:00``, “nanoseconds” are always positive. | ||
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| * Engines like Presto and Spark only support milliseconds precision, so |
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I believe Spark supports at least microseconds precision.
velox/docs/develop/timestamp.rst
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| 00:00:00``, “nanoseconds” are always positive. | ||
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| * Engines like Presto and Spark only support milliseconds precision, so | ||
| naturally “nanoseconds” are zeroed. |
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Nanoseconds are used even with millisecond precision.
velox/docs/develop/timestamp.rst
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| TimestampWithTimezones are serialized, for example. | ||
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| **TimestampWithTimezone:** To represent an absolute point in time, Velox provides | ||
| the `TimestampWithTimezone class <https://github.com/facebookincubator/velox/blob/main/velox/functions/prestosql/types/TimestampWithTimeZoneType.h>`_. |
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I don't think there is a TimestampWithTimezone class.
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well, it's an alias:
I'll rephrase.
velox/docs/develop/timestamp.rst
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| **TimestampWithTimezone:** To represent an absolute point in time, Velox provides | ||
| the `TimestampWithTimezone class <https://github.com/facebookincubator/velox/blob/main/velox/functions/prestosql/types/TimestampWithTimeZoneType.h>`_. | ||
| This class implements the TIMESTAMP WITH TIMEZONE sql semantic discussed above, |
velox/docs/develop/timestamp.rst
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| **TimestampWithTimezone:** To represent an absolute point in time, Velox provides | ||
| the `TimestampWithTimezone class <https://github.com/facebookincubator/velox/blob/main/velox/functions/prestosql/types/TimestampWithTimeZoneType.h>`_. | ||
| This class implements the TIMESTAMP WITH TIMEZONE sql semantic discussed above, | ||
| and was based on Presto’s implementation - therefore only supporting |
velox/docs/develop/timestamp.rst
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| millisecond-precision. | ||
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| TimestampWithTimezone physically packs two integers in a single 64 word, using | ||
| 12 bits for timezone ID, and 52 for a millisecond-precision timestamp. |
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| .. code-block:: bash | ||
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| $ rpm -qa | grep tzdata |
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I tried this command on my Mac, but it didn't print anything.
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this is for linux; added to the text to clarify
zacw7
approved these changes
Jun 5, 2024
velox/docs/develop/timestamp.rst
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| To represent absolute points in time, SQL defines a TIMESTAMP WITH TIMEZONE | ||
| type, which conceptually represents a pair of a wall time and calendar read | ||
| (say, ``2024-04-09 18:25:00``), and a timezone (``PST``, or |
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April should be in PDT instead of PST at America/Los_Angeles. Or we can just put PT here.
velox/docs/develop/timestamp.rst
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| .. code-block:: sql | ||
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| presto:de> select typeof(TIMESTAMP '1970-01-01 00:00:00'); |
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Let's omit the presto:de part? Should we keep the format of the examples consistent as https://facebookincubator.github.io/velox/functions/presto/conversion.html#cast-to-timestamp
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Nice! That's better
Adding a new documentation page to describe details of management of timestamp, timezone and conversions in Velox.
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Joe-Abraham
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Jun 7, 2024
…r#10036) Summary: Adding a new documentation page to describe details of management of timestamps, timezone and conversions in Velox. Pull Request resolved: facebookincubator#10036 Reviewed By: mbasmanova, zacw7 Differential Revision: D58172617 Pulled By: pedroerp fbshipit-source-id: a8fc2e5a78bd65bf587b65e3296ef3c27f23da28
Joe-Abraham
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Jun 7, 2024
…r#10036) Summary: Adding a new documentation page to describe details of management of timestamps, timezone and conversions in Velox. Pull Request resolved: facebookincubator#10036 Reviewed By: mbasmanova, zacw7 Differential Revision: D58172617 Pulled By: pedroerp fbshipit-source-id: a8fc2e5a78bd65bf587b65e3296ef3c27f23da28
deepashreeraghu
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Jun 13, 2024
…r#10036) Summary: Adding a new documentation page to describe details of management of timestamps, timezone and conversions in Velox. Pull Request resolved: facebookincubator#10036 Reviewed By: mbasmanova, zacw7 Differential Revision: D58172617 Pulled By: pedroerp fbshipit-source-id: a8fc2e5a78bd65bf587b65e3296ef3c27f23da28
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Adding a new documentation page to describe details of management of timestamps, timezone and conversions in Velox.