Fix NullArrayReader (#1245)#1246
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| self.rep_levels_buffer = self.record_reader.consume_rep_levels()?; | ||
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| // Must consume bitmap buffer | ||
| self.record_reader.consume_bitmap_buffer()?; |
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Why this is even getting computed at all is definitely a valid question, but at the same time a workload where the speed of reading arrays of nulls is the bottleneck feels decidedly... niche 😆
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One place it comes up is where you have multiple Parquet files representing a "table", with one or more columns being relatively sparse. If you have a file dropped every hour, then it may be that some of the files have a null column while others have a few values.
It doesn't seem likely it would be the bottleneck (the other columns in the file probably would be), but that's at least how it's come up for us.
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Yeah, I didn't mean to suggest NullArrayReader itself is niche, but rather there is probably a limited benefit to optimising it to not compute the bitmask unnecessarily 😄
alamb
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Thanks @tustvold -- I'll get this out in arrow 9.0.0 next week; I can try to release a patchset sooner if you need @bjchambers
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No need to rush. Next week should be fine. I can just wait to upgrade until
this is out. Thanks for the speedy fix!
…On Sat, Jan 29, 2022 at 3:19 AM Andrew Lamb ***@***.***> wrote:
***@***.**** approved this pull request.
Thanks @tustvold <https://github.com/tustvold> -- I'll get this out in
arrow 9.0.0 next week; I can try to release a patchset sooner if you need
@bjchambers <https://github.com/bjchambers>
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Which issue does this PR close?
Closes #1245.
Rationale for this change
Originally reported by @bjchambers, a sanity check added in #1054 fires when reading NullArrays.
This highlighted two problems:
NullArrayReaderhas always been somewhat broken as it would never flush the accumulated null buffer, instead just growing it indefinitelyWhat changes are included in this PR?
Fixes the panic, and adds a basic test of the
NullArrayReaderAre there any user-facing changes?
NullArrayReader should work again