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API

The API is a single function ingest, together with classes of string constants: HighWatermark, Visibility, Upsert and Delete. The constants are known strings rather than opaque identifiers to allow the strings to be easily passed from dynamic/non-Python environments.

ingest(conn, metadata, batches, on_before_visible=lambda conn, latest_batch_metadata: None, high_watermark=HighWatermark.LATEST, visibility=Visibility.AFTER_EACH_BATCH, upsert=Upsert.IF_PRIMARY_KEY, delete=Delete.OFF, max_rows_per_table_buffer=10000)

Ingests data into a table

  • conn - A SQLAlchemy connection not in a transaction, i.e. started by connection rather than begin.

  • metadata - A SQLAlchemy metadata of one or more tables.

  • batches - A function that takes a high watermark, returning an iterable that yields data batches that are strictly after this high watermark. See Usage above for an example.

  • on_before_visible (optional) - A function that takes a SQLAlchemy connection in a transaction and batch metadata, called just before data becomes visible to other database clients. See Usage above for an example.

  • high_watermark (optional) - A member of the HighWatermark class, or a JSON-encodable value.

    If this is HighWatermark.LATEST, then the most recent high watermark that been returned from a previous ingest’s batch function whose corresponding batch has been succesfully ingested is passed into the batches function. If there has been no previous ingest, None will be passed.

    If this is HighWatermark.EARLIEST, then None will be passed to the batches function as the high watermark. This would typically be used to re-ingest all of the data.

    If this a JSON-encodable value other than HighWatermark.LATEST or HighWatermark.EARLIEST, then this value is passed directly to the batches function. This can be used to override any previous high-watermark. Existing data in the target table is not deleted unless specified by the delete parameter.

  • visibility (optional) - A member of the Visibilty class, controlling when ingests will be visible to other clients.

  • upsert (optional) - A member of the Upsert class, controlling whether an upsert is performed when ingesting data

  • delete (optional) - A member of the Delete class, controlling if existing rows are to be deleted.

  • max_rows_per_table_buffer (optional) - An integer number of rows to buffer in memory per table when ingesting into multiple tables.

HighWatermark

A class of constants to indicate what high watermark should be passed into the batches function.

  • LATEST - pass the most recent high watermark yielded from the batches function from the previous ingest into the batches function. If there is no previous ingest, the Python value None is passed. This is the string __LATEST__.

  • EARLIEST - pass the Python value None into the batches function. This is the string __EARLIEST__.

Visibility

A class of constants to indicate when data changes are visible to other database clients. Schema changes become visible before the first batch.

  • AFTER_EACH_BATCH - data changes are visible to other database clients after each batch. This is the string __AFTER_EACH_BATCH__.

Delete

A class of constants that controls how existing data in the table is deleted

  • OFF

    There is no deleting of existing data. This is the string __OFF__.

  • BEFORE_FIRST_BATCH

    All existing data in the table is deleted just before the first batch is ingested. If there are no batches, no data is deleted. This is the string __BEFORE_FIRST_BATCH__.

Upsert

A class of constants that controls if upserting is performed

  • OFF

    No upserting is performed. This is the string __OFF__.

  • IF_PRIMARY_KEY

    If the table contains a primary key, an upsert based on that primary key is performed on ingest. If there is no primary key then a plain insert is performed. This is useful to avoid duplication if batches overlap. This is the string __IF_PRIMARY_KEY__.