zachdisc commented on PR #9731:
URL: https://github.com/apache/iceberg/pull/9731#issuecomment-1961864865
## Rev 3
* Addressed last round of comments
* Added a new API option to sort with a custom supplied
`Function<DataFile>`.
Illustration (in unit test) - say you have a table that is partitioned by
`a, truncate(b, 5), bucket(10, c)`. We can choose to re-organize manifests
around `c`, such that we have roughly half of the `c` partitions contained in
individual `manifest_list` tree entry.
So supply a Function like below, which checks if the `c` partition value is
< 5 and returns a string.
```
Function<DataFile, String> test =
(Function<DataFile, String> & Serializable)
(dataFile) -> {
StructLike partition = dataFile.partition();
// Find the ordinal index for the c3 partition column for this
data file
int c3Index =
IntStream.range(0, spec.fields().size())
.filter(i ->
spec.fields().get(i).name().contains("c3"))
.findFirst()
.getAsInt();
Object c3BucketValue = partition.get(c3Index, Object.class);
// Return one string for the lower values, one for the upper.
RewriteManifests
// will cluster datafiles together in manifests according to
this value.
return (Integer) c3BucketValue < 5 ? "cluster=LT_5" :
"cluster=GTE_5";
};
```
The value used for repartitioning/sorting on will fall into two values. One
where the transformed bucket value is less than 5, one for values over 5.
Illustration of the partition set for a data file vs this new supplied
clustering column value
```
+--------------------+---------------------+
|partition |__clustering_column__|
+--------------------+---------------------+
|{0, -531806488, 0} |cluster=LT_5 |. <-- the last partition value
for `c` is 0. Which is labeled as "LT_5"
|{1, 385955472, 7} |cluster=GTE_5 |
|{2, 604077840, 6} |cluster=GTE_5 |
|{3, 1875302972, 4} |cluster=LT_5 |
|{4, -1772544904, 0} |cluster=LT_5 |
+--------------------+---------------------+
```
Rewritten manifests will group manifest_file s by having data files within
that map to `c` partition values from 0-4 and 5-9
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