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https://issues.apache.org/jira/browse/ARROW-5324?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17662345#comment-17662345
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Rok Mihevc commented on ARROW-5324:
-----------------------------------
This issue has been migrated to [issue
#21786|https://github.com/apache/arrow/issues/21786] on GitHub. Please see the
[migration documentation|https://github.com/apache/arrow/issues/14542] for
further details.
> [Plasma] API requests
> ---------------------
>
> Key: ARROW-5324
> URL: https://issues.apache.org/jira/browse/ARROW-5324
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C++ - Plasma
> Reporter: Darren Weber
> Priority: Minor
>
> Copied from [https://github.com/apache/arrow/issues/4318] (it's easier to
> read there, sorry hate Jira formatting)
> Related to https://issues.apache.org/jira/browse/ARROW-3444
> While working with the plasma API to create/seal an object for a table, using
> a custom object-ID, it would help to have a convenience API to get the size
> of the table.
> The following code might help to illustrate the request and notes below:
> {code:java}
> if not parquet_path:
> parquet_path = f"./data/dataset_{size}.parquet"
> if not plasma_path:
> plasma_path = f"./data/dataset_{size}.plasma"
> try:
> plasma_client = plasma.connect(plasma_path)
> except:
> plasma_client = None
> if plasma_client:
> table_id = plasma.ObjectID(bytes(parquet_path[:20], encoding='utf8'))
> try:
> table = plasma_client.get(table_id, timeout_ms=4000)
> if table.__name__ == 'ObjectNotAvailable':
> raise ValueError('Failed to get plasma object')
> except ValueError:
> table = pq.read_table(parquet_path, use_threads=True)
> plasma_client.create_and_seal(table_id, table)
> {code}
>
> The use case is a workflow something like this:
> - process-A
> ** generate a pandas DataFrame `df`
> ** save the `df` to parquet, using pyarrow.parquet, with a unique parquet
> path
> ** (this process will not save directly to plasma)
> - process-B
> ** get the data from plasma or load it into plasma from the parquet file
> ** use the unique parquet path to generate a unique object-ID
> Notes:
> - `plasma_client.put` for the same data-table is not idempotent, it
> generates unique object-ID values that are not based on any hash of the data
> payload, so every put saves a new object-ID; could it use a data hash for
> idempotent puts? e.g.
> -
> {code:java}
> In : plasma_client.put(table)
> ObjectID(666625fcb60959d23b6bfc739f88816da29e04d6)
> In : plasma_client.put(table)
> ObjectID(d2a4662999db30177b090f9fc2bf6b28687d2f8d)
> In : plasma_client.put(table)
> ObjectID(b2928ad786de2fdb74d374055597f6e7bd97fd61)
> In : hash(table)
> TypeError: unhashable type: 'pyarrow.lib.Table'{code}
> - In process-B, when the data is not already in plasma, it reads data from a
> parquet file into a pyarrow.Table and then needs an object-ID and the table
> size to use plasma `client.create_and_seal` but it's not easy to get the
> table size - this might be related to github issue #2707 (#3444) - it might
> be ideal if the `client.create_and_seal` accepts responsibility for the size
> of the object to be created when given a pyarrow data object like a table.
> - when the plasma store does not have the object, it could have a default
> timeout rather than hang indefinitely, and it's a bit clumsy to return an
> object that is not easily checked with `isinstance` and it could be better to
> have an exception handling pattern (or something like the requests 404
> patterns and options?)
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