[jira] [Comment Edited] (PARQUET-2249) Parquet spec (parquet.thrift) is inconsistent w.r.t. ColumnIndex + NaNs
[
https://issues.apache.org/jira/browse/PARQUET-2249?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel=17691525#comment-17691525
]
Jan Finis edited comment on PARQUET-2249 at 2/21/23 11:19 AM:
--
[~wgtmac] my proposal would be backward compatible. It would only add optional
fields, so that legacy readers not implementing the logic could still read the
file and legacy writers could also still write files not using this without any
code changes.
[~mwish] I agree. Treating NaN as larger or smaller than any other value
doesn't fit the semantics of all engines. Therefore, my fix for this would
enable both types of semantics (and a third semantics, where NaN should be
treated as neither larger nor smaller) to work.
I guess I'll just create a pull request. We can then start the discussion based
on this. Sounds good?
was (Author: jfinis):
[~wgtmac] my proposal would be backward compatible. It would only add optional
fields, so that legacy readers not implementing the logic could still read the
file and legacy writers could also still write files not using this without any
code changes.
> Parquet spec (parquet.thrift) is inconsistent w.r.t. ColumnIndex + NaNs
> ---
>
> Key: PARQUET-2249
> URL: https://issues.apache.org/jira/browse/PARQUET-2249
> Project: Parquet
> Issue Type: Bug
> Components: parquet-format
>Reporter: Jan Finis
>Priority: Major
>
> Currently, the specification of {{ColumnIndex}} in {{parquet.thrift}} is
> inconsistent, leading to cases where it is impossible to create a parquet
> file that is conforming to the spec.
> The problem is with double/float columns if a page contains only NaN values.
> The spec mentions that NaN values should not be included in min/max bounds,
> so a page consisting of only NaN values has no defined min/max bound. To
> quote the spec:
> {noformat}
> * When writing statistics the following rules should be followed:
> * - NaNs should not be written to min or max statistics
> fields.{noformat}
> However, the comments in the ColumnIndex on the null_pages member states the
> following:
> {noformat}
> struct ColumnIndex {
> /**
> * A list of Boolean values to determine the validity of the corresponding
> * min and max values. If true, a page contains only null values, and
> writers
> * have to set the corresponding entries in min_values and max_values to
> * byte[0], so that all lists have the same length. If false, the
> * corresponding entries in min_values and max_values must be valid.
> */
> 1: required list null_pages{noformat}
> For a page with only NaNs, we now have a problem. The page definitly does
> *not* only contain null values, so {{null_pages}} should be {{false}} for
> this page. However, in this case the spec requires valid min/max values in
> {{min_values}} and {{max_values}} for this page. As the only value in the
> page is NaN, the only valid min/max value we could enter here is NaN, but as
> mentioned before, NaNs should never be written to min/max values.
> Thus, no writer can currently create a parquet file that conforms to this
> specification as soon as there is a only-NaN column and column indexes are to
> be written.
> I see three possible solutions:
> 1. A page consisting only of NaNs (or a mixture of NaNs and nulls) has it's
> null_pages entry set to {*}true{*}.
> 2. A page consisting of only NaNs (or a mixture of NaNs and nulls) has
> {{byte[0]}} as min/max, even though the null_pages entry is set to
> {*}false{*}.
> 3. A page consisting of only NaNs (or a mixture of NaNs and nulls) does have
> NaN as min & max in the column index.
> None of the solutions is perfect. But I guess solution 3. is the best of
> them. It gives us valid min/max bounds, makes null_pages compatible with
> this, and gives us a way to determine only-Nan pages (min=max=NaN).
> As a general note: I would say that it is a shortcoming that Parquet doesn't
> track NaN counts. E.g., Iceberg does track NaN counts and therefore doesn't
> have this inconsistency. In a future version, NaN counts could be introduced,
> but that doesn't help for backward compatibility, so we do need a solution
> for now.
> Any of the solutions is better than the current situation where engines
> writing such a page cannot write a conforming parquet file and will randomly
> pick any of the solutions.
> Thus, my suggestion would be to update parquet.thrift to use solution 3.
> I.e., rewrite the comments saying that NaNs shouldn't be included in min/max
> bounds by adding a clause stating that "if a page contains only NaNs or a
> mixture of NaNs and NULLs, then NaN should be written as min & max".
>
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[jira] [Comment Edited] (PARQUET-2249) Parquet spec (parquet.thrift) is inconsistent w.r.t. ColumnIndex + NaNs
[
https://issues.apache.org/jira/browse/PARQUET-2249?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel=17691184#comment-17691184
]
Jan Finis edited comment on PARQUET-2249 at 2/20/23 1:50 PM:
-
I would be willing to propose a fixing commit for this, but I'm not part of ASF
and the whole process, yet, so I don't know exactly how to get that going. I
could start a PR on the parquet-format github repo. Is that the right point to
suggest changes to the spec/parquet.thrift?
Sidepoint: Note that NaN being larger than all other values is also:
* The semantic that SQL has for NaN
* What parquet-mr seems to be doing right now. At least, I have found parquet
files that have NaN written as max_value in row group statistics.
However, treating NaN as something extra by maintaining NaN counts will allow
incorporating any NaN semantics the query engine wishes to use.
was (Author: jfinis):
I would be willing to propose a fixing commit for this, but I'm not part of ASF
and the whole process, yet, so I don't know exactly how to get that going. I
could start a PR on the parquet-format github repo. Is that the right point to
suggest changes to the spec/parquet.thrift?
Note that NaN being larger than all other values is also:
* The semantic that SQL has for NaN
* What parquet-mr seems to be doing right now. At least, I have found parquet
files that have NaN written as max_value in row group statistics.
> Parquet spec (parquet.thrift) is inconsistent w.r.t. ColumnIndex + NaNs
> ---
>
> Key: PARQUET-2249
> URL: https://issues.apache.org/jira/browse/PARQUET-2249
> Project: Parquet
> Issue Type: Bug
> Components: parquet-format
>Reporter: Jan Finis
>Priority: Major
>
> Currently, the specification of {{ColumnIndex}} in {{parquet.thrift}} is
> inconsistent, leading to cases where it is impossible to create a parquet
> file that is conforming to the spec.
> The problem is with double/float columns if a page contains only NaN values.
> The spec mentions that NaN values should not be included in min/max bounds,
> so a page consisting of only NaN values has no defined min/max bound. To
> quote the spec:
> {noformat}
> * When writing statistics the following rules should be followed:
> * - NaNs should not be written to min or max statistics
> fields.{noformat}
> However, the comments in the ColumnIndex on the null_pages member states the
> following:
> {noformat}
> struct ColumnIndex {
> /**
> * A list of Boolean values to determine the validity of the corresponding
> * min and max values. If true, a page contains only null values, and
> writers
> * have to set the corresponding entries in min_values and max_values to
> * byte[0], so that all lists have the same length. If false, the
> * corresponding entries in min_values and max_values must be valid.
> */
> 1: required list null_pages{noformat}
> For a page with only NaNs, we now have a problem. The page definitly does
> *not* only contain null values, so {{null_pages}} should be {{false}} for
> this page. However, in this case the spec requires valid min/max values in
> {{min_values}} and {{max_values}} for this page. As the only value in the
> page is NaN, the only valid min/max value we could enter here is NaN, but as
> mentioned before, NaNs should never be written to min/max values.
> Thus, no writer can currently create a parquet file that conforms to this
> specification as soon as there is a only-NaN column and column indexes are to
> be written.
> I see three possible solutions:
> 1. A page consisting only of NaNs (or a mixture of NaNs and nulls) has it's
> null_pages entry set to {*}true{*}.
> 2. A page consisting of only NaNs (or a mixture of NaNs and nulls) has
> {{byte[0]}} as min/max, even though the null_pages entry is set to
> {*}false{*}.
> 3. A page consisting of only NaNs (or a mixture of NaNs and nulls) does have
> NaN as min & max in the column index.
> None of the solutions is perfect. But I guess solution 3. is the best of
> them. It gives us valid min/max bounds, makes null_pages compatible with
> this, and gives us a way to determine only-Nan pages (min=max=NaN).
> As a general note: I would say that it is a shortcoming that Parquet doesn't
> track NaN counts. E.g., Iceberg does track NaN counts and therefore doesn't
> have this inconsistency. In a future version, NaN counts could be introduced,
> but that doesn't help for backward compatibility, so we do need a solution
> for now.
> Any of the solutions is better than the current situation where engines
> writing such a page cannot write a conforming parquet file and will randomly
> pick any of the solutions.
> Thus, my suggestion would be to update parquet.thrift to use solution 3.
>
[jira] [Comment Edited] (PARQUET-2249) Parquet spec (parquet.thrift) is inconsistent w.r.t. ColumnIndex + NaNs
[
https://issues.apache.org/jira/browse/PARQUET-2249?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel=17691184#comment-17691184
]
Jan Finis edited comment on PARQUET-2249 at 2/20/23 1:48 PM:
-
I would be willing to propose a fixing commit for this, but I'm not part of ASF
and the whole process, yet, so I don't know exactly how to get that going. I
could start a PR on the parquet-format github repo. Is that the right point to
suggest changes to the spec/parquet.thrift?
Note that NaN being larger than all other values is also:
* The semantic that SQL has for NaN
* What parquet-mr seems to be doing right now. At least, I have found parquet
files that have NaN written as max_value in row group statistics.
was (Author: jfinis):
I would be willing to suggest a fix for this, but I'm not part of ASF and the
whole process, yet, so I don't know exactly how to get that going. I could
start a PR on the parquet-format github repo. Is that the right point to
suggest changes to the spec/parquet.thrift?
Note that NaN being larger than all other values is also:
* The semantic that SQL has for NaN
* What parquet-mr seems to be doing right now. At least, I have found parquet
files that have NaN written as max_value in row group statistics.
> Parquet spec (parquet.thrift) is inconsistent w.r.t. ColumnIndex + NaNs
> ---
>
> Key: PARQUET-2249
> URL: https://issues.apache.org/jira/browse/PARQUET-2249
> Project: Parquet
> Issue Type: Bug
> Components: parquet-format
>Reporter: Jan Finis
>Priority: Major
>
> Currently, the specification of {{ColumnIndex}} in {{parquet.thrift}} is
> inconsistent, leading to cases where it is impossible to create a parquet
> file that is conforming to the spec.
> The problem is with double/float columns if a page contains only NaN values.
> The spec mentions that NaN values should not be included in min/max bounds,
> so a page consisting of only NaN values has no defined min/max bound. To
> quote the spec:
> {noformat}
> * When writing statistics the following rules should be followed:
> * - NaNs should not be written to min or max statistics
> fields.{noformat}
> However, the comments in the ColumnIndex on the null_pages member states the
> following:
> {noformat}
> struct ColumnIndex {
> /**
> * A list of Boolean values to determine the validity of the corresponding
> * min and max values. If true, a page contains only null values, and
> writers
> * have to set the corresponding entries in min_values and max_values to
> * byte[0], so that all lists have the same length. If false, the
> * corresponding entries in min_values and max_values must be valid.
> */
> 1: required list null_pages{noformat}
> For a page with only NaNs, we now have a problem. The page definitly does
> *not* only contain null values, so {{null_pages}} should be {{false}} for
> this page. However, in this case the spec requires valid min/max values in
> {{min_values}} and {{max_values}} for this page. As the only value in the
> page is NaN, the only valid min/max value we could enter here is NaN, but as
> mentioned before, NaNs should never be written to min/max values.
> Thus, no writer can currently create a parquet file that conforms to this
> specification as soon as there is a only-NaN column and column indexes are to
> be written.
> I see three possible solutions:
> 1. A page consisting only of NaNs (or a mixture of NaNs and nulls) has it's
> null_pages entry set to {*}true{*}.
> 2. A page consisting of only NaNs (or a mixture of NaNs and nulls) has
> {{byte[0]}} as min/max, even though the null_pages entry is set to
> {*}false{*}.
> 3. A page consisting of only NaNs (or a mixture of NaNs and nulls) does have
> NaN as min & max in the column index.
> None of the solutions is perfect. But I guess solution 3. is the best of
> them. It gives us valid min/max bounds, makes null_pages compatible with
> this, and gives us a way to determine only-Nan pages (min=max=NaN).
> As a general note: I would say that it is a shortcoming that Parquet doesn't
> track NaN counts. E.g., Iceberg does track NaN counts and therefore doesn't
> have this inconsistency. In a future version, NaN counts could be introduced,
> but that doesn't help for backward compatibility, so we do need a solution
> for now.
> Any of the solutions is better than the current situation where engines
> writing such a page cannot write a conforming parquet file and will randomly
> pick any of the solutions.
> Thus, my suggestion would be to update parquet.thrift to use solution 3.
> I.e., rewrite the comments saying that NaNs shouldn't be included in min/max
> bounds by adding a clause stating that "if a page contains only NaNs or a
> mixture of
[jira] [Comment Edited] (PARQUET-2249) Parquet spec (parquet.thrift) is inconsistent w.r.t. ColumnIndex + NaNs
[
https://issues.apache.org/jira/browse/PARQUET-2249?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel=17691184#comment-17691184
]
Jan Finis edited comment on PARQUET-2249 at 2/20/23 1:48 PM:
-
I would be willing to suggest a fix for this, but I'm not part of ASF and the
whole process, yet, so I don't know exactly how to get that going. I could
start a PR on the parquet-format github repo. Is that the right point to
suggest changes to the spec/parquet.thrift?
Note that NaN being larger than all other values is also:
* The semantic that SQL has for NaN
* What parquet-mr seems to be doing right now. At least, I have found parquet
files that have NaN written as max_value in row group statistics.
was (Author: jfinis):
I would be willing to suggest a fix for this, but I'm not part of ASF and the
whole process, yet, so I don't know exactly how to get that going. I could
start a PR on the parquet-mr github repo. Is that the right point to suggest
changes to the spec/parquet.thrift?
> Parquet spec (parquet.thrift) is inconsistent w.r.t. ColumnIndex + NaNs
> ---
>
> Key: PARQUET-2249
> URL: https://issues.apache.org/jira/browse/PARQUET-2249
> Project: Parquet
> Issue Type: Bug
> Components: parquet-format
>Reporter: Jan Finis
>Priority: Major
>
> Currently, the specification of {{ColumnIndex}} in {{parquet.thrift}} is
> inconsistent, leading to cases where it is impossible to create a parquet
> file that is conforming to the spec.
> The problem is with double/float columns if a page contains only NaN values.
> The spec mentions that NaN values should not be included in min/max bounds,
> so a page consisting of only NaN values has no defined min/max bound. To
> quote the spec:
> {noformat}
> * When writing statistics the following rules should be followed:
> * - NaNs should not be written to min or max statistics
> fields.{noformat}
> However, the comments in the ColumnIndex on the null_pages member states the
> following:
> {noformat}
> struct ColumnIndex {
> /**
> * A list of Boolean values to determine the validity of the corresponding
> * min and max values. If true, a page contains only null values, and
> writers
> * have to set the corresponding entries in min_values and max_values to
> * byte[0], so that all lists have the same length. If false, the
> * corresponding entries in min_values and max_values must be valid.
> */
> 1: required list null_pages{noformat}
> For a page with only NaNs, we now have a problem. The page definitly does
> *not* only contain null values, so {{null_pages}} should be {{false}} for
> this page. However, in this case the spec requires valid min/max values in
> {{min_values}} and {{max_values}} for this page. As the only value in the
> page is NaN, the only valid min/max value we could enter here is NaN, but as
> mentioned before, NaNs should never be written to min/max values.
> Thus, no writer can currently create a parquet file that conforms to this
> specification as soon as there is a only-NaN column and column indexes are to
> be written.
> I see three possible solutions:
> 1. A page consisting only of NaNs (or a mixture of NaNs and nulls) has it's
> null_pages entry set to {*}true{*}.
> 2. A page consisting of only NaNs (or a mixture of NaNs and nulls) has
> {{byte[0]}} as min/max, even though the null_pages entry is set to
> {*}false{*}.
> 3. A page consisting of only NaNs (or a mixture of NaNs and nulls) does have
> NaN as min & max in the column index.
> None of the solutions is perfect. But I guess solution 3. is the best of
> them. It gives us valid min/max bounds, makes null_pages compatible with
> this, and gives us a way to determine only-Nan pages (min=max=NaN).
> As a general note: I would say that it is a shortcoming that Parquet doesn't
> track NaN counts. E.g., Iceberg does track NaN counts and therefore doesn't
> have this inconsistency. In a future version, NaN counts could be introduced,
> but that doesn't help for backward compatibility, so we do need a solution
> for now.
> Any of the solutions is better than the current situation where engines
> writing such a page cannot write a conforming parquet file and will randomly
> pick any of the solutions.
> Thus, my suggestion would be to update parquet.thrift to use solution 3.
> I.e., rewrite the comments saying that NaNs shouldn't be included in min/max
> bounds by adding a clause stating that "if a page contains only NaNs or a
> mixture of NaNs and NULLs, then NaN should be written as min & max".
>
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[jira] [Comment Edited] (PARQUET-2249) Parquet spec (parquet.thrift) is inconsistent w.r.t. ColumnIndex + NaNs
[
https://issues.apache.org/jira/browse/PARQUET-2249?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel=17691179#comment-17691179
]
Xuwei Fu edited comment on PARQUET-2249 at 2/20/23 1:30 PM:
The problem seem to be that, float point is so widely used, but they are
"partial order". Seems that iceberg provides NaN counts. And min-max is
un-related to NaN.
In Sorting, iceberg forces that:
> Sorting floating-point numbers should produce the following behavior:
> {{-NaN}} < {{-Infinity}} < {{-value}} < {{-0}} < {{0}} < {{value}} <
> {{Infinity}} < {{{}NaN{}}}. This aligns with the implementation of Java
> floating-point types comparisons.
I think (1) is bad, because NaN is never equal to NULL.
IEEE754 ([https://ieeexplore.ieee.org/document/8766229]) and C++ standard
support some "totalOrder", but I think regard it as totalOrder is strange, so
min-max as `byte[0]` is wierd for me. I think iceberg style looks great
If I'm wrong, please correct me
was (Author: JIRAUSER294084):
Seems that iceberg provides NaN counts. And min-max is un-related to NaN.
In Sorting, iceberg forces that:
> Sorting floating-point numbers should produce the following behavior:
> {{-NaN}} < {{-Infinity}} < {{-value}} < {{-0}} < {{0}} < {{value}} <
> {{Infinity}} < {{{}NaN{}}}. This aligns with the implementation of Java
> floating-point types comparisons.
I think (1) is bad, because NaN is never equal to NULL.
IEEE754 (https://ieeexplore.ieee.org/document/8766229) and C++ standard support
some "totalOrder", but I think regard it as totalOrder is strange, so min-max
as `byte[0]` is wierd for me. I think iceberg style looks great
> Parquet spec (parquet.thrift) is inconsistent w.r.t. ColumnIndex + NaNs
> ---
>
> Key: PARQUET-2249
> URL: https://issues.apache.org/jira/browse/PARQUET-2249
> Project: Parquet
> Issue Type: Bug
> Components: parquet-format
>Reporter: Jan Finis
>Priority: Major
>
> Currently, the specification of {{ColumnIndex}} in {{parquet.thrift}} is
> inconsistent, leading to cases where it is impossible to create a parquet
> file that is conforming to the spec.
> The problem is with double/float columns if a page contains only NaN values.
> The spec mentions that NaN values should not be included in min/max bounds,
> so a page consisting of only NaN values has no defined min/max bound. To
> quote the spec:
> {noformat}
> * When writing statistics the following rules should be followed:
> * - NaNs should not be written to min or max statistics
> fields.{noformat}
> However, the comments in the ColumnIndex on the null_pages member states the
> following:
> {noformat}
> struct ColumnIndex {
> /**
> * A list of Boolean values to determine the validity of the corresponding
> * min and max values. If true, a page contains only null values, and
> writers
> * have to set the corresponding entries in min_values and max_values to
> * byte[0], so that all lists have the same length. If false, the
> * corresponding entries in min_values and max_values must be valid.
> */
> 1: required list null_pages{noformat}
> For a page with only NaNs, we now have a problem. The page definitly does
> *not* only contain null values, so {{null_pages}} should be {{false}} for
> this page. However, in this case the spec requires valid min/max values in
> {{min_values}} and {{max_values}} for this page. As the only value in the
> page is NaN, the only valid min/max value we could enter here is NaN, but as
> mentioned before, NaNs should never be written to min/max values.
> Thus, no writer can currently create a parquet file that conforms to this
> specification as soon as there is a only-NaN column and column indexes are to
> be written.
> I see three possible solutions:
> 1. A page consisting only of NaNs (or a mixture of NaNs and nulls) has it's
> null_pages entry set to {*}true{*}.
> 2. A page consisting of only NaNs (or a mixture of NaNs and nulls) has
> {{byte[0]}} as min/max, even though the null_pages entry is set to
> {*}false{*}.
> 3. A page consisting of only NaNs (or a mixture of NaNs and nulls) does have
> NaN as min & max in the column index.
> None of the solutions is perfect. But I guess solution 3. is the best of
> them. It gives us valid min/max bounds, makes null_pages compatible with
> this, and gives us a way to determine only-Nan pages (min=max=NaN).
> As a general note: I would say that it is a shortcoming that Parquet doesn't
> track NaN counts. E.g., Iceberg does track NaN counts and therefore doesn't
> have this inconsistency. In a future version, NaN counts could be introduced,
> but that doesn't help for backward compatibility, so we do need a solution
> for now.
> Any of the solutions is better than the
[jira] [Comment Edited] (PARQUET-2249) Parquet spec (parquet.thrift) is inconsistent w.r.t. ColumnIndex + NaNs
[
https://issues.apache.org/jira/browse/PARQUET-2249?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel=17691108#comment-17691108
]
Jan Finis edited comment on PARQUET-2249 at 2/20/23 9:55 AM:
-
[~wgtmac] True, not writing a column index in this case is also a solution.
Note though that this is a pessimization for pages not containing NaN in the
same column chunk. It would be a shame if a single NaN makes a whole column
chunk non-indexable. It might be a good interim solution, but it's not too
satisfying.
The whole topic of NaN handling in Parquet currently seems to be lacking and
somewhat inconsistent, making columns with NaNs mostly unusable for scan
pruning. Maybe there should be a redefinition of the semantics in a new
version, so that columns with NaNs can be used for indexing as other columns.
As mentioned, Iceberg has solved this problem by providing NaN counts.
was (Author: jfinis):
[~wgtmac] True, not writing a column index in this case is also a solution.
Note though that this is a pessimization for pages not containing NaN in the
same column chunk. It would be a shame if a single NaN makes a whole column
chunk non-indexable. It might be a good interim solution, but it's not too
satisfying.
> Parquet spec (parquet.thrift) is inconsistent w.r.t. ColumnIndex + NaNs
> ---
>
> Key: PARQUET-2249
> URL: https://issues.apache.org/jira/browse/PARQUET-2249
> Project: Parquet
> Issue Type: Bug
> Components: parquet-format
>Reporter: Jan Finis
>Priority: Major
>
> Currently, the specification of {{ColumnIndex}} in {{parquet.thrift}} is
> inconsistent, leading to cases where it is impossible to create a parquet
> file that is conforming to the spec.
> The problem is with double/float columns if a page contains only NaN values.
> The spec mentions that NaN values should not be included in min/max bounds,
> so a page consisting of only NaN values has no defined min/max bound. To
> quote the spec:
> {noformat}
> * When writing statistics the following rules should be followed:
> * - NaNs should not be written to min or max statistics
> fields.{noformat}
> However, the comments in the ColumnIndex on the null_pages member states the
> following:
> {noformat}
> struct ColumnIndex {
> /**
> * A list of Boolean values to determine the validity of the corresponding
> * min and max values. If true, a page contains only null values, and
> writers
> * have to set the corresponding entries in min_values and max_values to
> * byte[0], so that all lists have the same length. If false, the
> * corresponding entries in min_values and max_values must be valid.
> */
> 1: required list null_pages{noformat}
> For a page with only NaNs, we now have a problem. The page definitly does
> *not* only contain null values, so {{null_pages}} should be {{false}} for
> this page. However, in this case the spec requires valid min/max values in
> {{min_values}} and {{max_values}} for this page. As the only value in the
> page is NaN, the only valid min/max value we could enter here is NaN, but as
> mentioned before, NaNs should never be written to min/max values.
> Thus, no writer can currently create a parquet file that conforms to this
> specification as soon as there is a only-NaN column and column indexes are to
> be written.
> I see three possible solutions:
> 1. A page consisting only of NaNs (or a mixture of NaNs and nulls) has it's
> null_pages entry set to {*}true{*}.
> 2. A page consisting of only NaNs (or a mixture of NaNs and nulls) has
> {{byte[0]}} as min/max, even though the null_pages entry is set to
> {*}false{*}.
> 3. A page consisting of only NaNs (or a mixture of NaNs and nulls) does have
> NaN as min & max in the column index.
> None of the solutions is perfect. But I guess solution 3. is the best of
> them. It gives us valid min/max bounds, makes null_pages compatible with
> this, and gives us a way to determine only-Nan pages (min=max=NaN).
> As a general note: I would say that it is a shortcoming that Parquet doesn't
> track NaN counts. E.g., Iceberg does track NaN counts and therefore doesn't
> have this inconsistency. In a future version, NaN counts could be introduced,
> but that doesn't help for backward compatibility, so we do need a solution
> for now.
> Any of the solutions is better than the current situation where engines
> writing such a page cannot write a conforming parquet file and will randomly
> pick any of the solutions.
> Thus, my suggestion would be to update parquet.thrift to use solution 3.
> I.e., rewrite the comments saying that NaNs shouldn't be included in min/max
> bounds by adding a clause stating that "if a page contains only NaNs or a
> mixture of NaNs and NULLs, then
