[ https://issues.apache.org/jira/browse/ARROW-8061?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17056248#comment-17056248 ]
Joris Van den Bossche commented on ARROW-8061: ---------------------------------------------- > Note that parallelism of RowGroup is already achieved since we return "1 row > group == 1 scantask" Yes, but for external users, it might be better to work on the level of fragments, rather than scan tasks? (eg, from the discussions, I had understood that serializing/reconstructing a scantask won't be possible. While for a fragment (or single-fragment dataset), this is posstible) > [C++][Dataset] Ability to specify granularity of ParquetFileFragment (support > row groups) > ----------------------------------------------------------------------------------------- > > Key: ARROW-8061 > URL: https://issues.apache.org/jira/browse/ARROW-8061 > Project: Apache Arrow > Issue Type: Improvement > Components: C++ - Dataset > Reporter: Joris Van den Bossche > Priority: Major > > Specifically for parquet (not sure if it will be relevant for other file > formats as well, for IPC/feather potentially ther record batch), it would be > useful to target row groups instead of files as fragments. > Quoting the original design documents: _"In datasets consisting of many > fragments, the dataset API must expose the granularity of fragments in a > public way to enable parallel processing, if desired. "._ > And a comment from Wes on that: _"a single Parquet file can "export" one or > more fragments based on settings. The default might be to split fragments > based on row group"_ > Currently, the level on which fragments are defined (at least in the typical > partitioned parquet dataset) is "1 file == 1 fragment". > Would it be possible or desirable to make this more fine grained, where you > could also opt to have a fragment per row group? > We could have a ParquetFragment that has this option, and a ParquetFileFormat > specific option to say what the granularity of a fragment is (file vs row > group)? > cc [~fsaintjacques] [~bkietz] -- This message was sent by Atlassian Jira (v8.3.4#803005)