RussellSpitzer commented on code in PR #12840:
URL: https://github.com/apache/iceberg/pull/12840#discussion_r2054920719
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api/src/main/java/org/apache/iceberg/actions/RewriteManifests.java:
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@@ -44,6 +45,28 @@ public interface RewriteManifests
*/
RewriteManifests rewriteIf(Predicate<ManifestFile> predicate);
+ /**
+ * Rewrite manifests in a given order, based on partition field names
+ *
+ * <p>Supply an optional set of partition field names to cluster the
rewritten manifests by. For
+ * example, given a table PARTITIONED BY (a, b, c, d), one may wish to
rewrite and cluster
+ * manifests by ('d', 'b') only, based on known query patterns. Rewriting
Manifests in this way
+ * will yield manifest_lists that point to manifest_files containing data
files for common 'd' and
+ * 'b' partitions.
+ *
+ * <p>If not set, manifests will be rewritten in the order of the transforms
in the table's
+ * current partition spec.
+ *
+ * @param partitionFields Exact transformed column names used for
partitioning; not the raw column
+ * names that partitions are derived from. E.G. supply 'data_bucket' and
not 'data' for a
+ * bucket(N, data) partition * definition
+ * @return this for method chaining
+ */
+ default RewriteManifests clusterBy(List<String> partitionFields) {
Review Comment:
Hmm that's a good question. In my eyes we are doing a hierarchical sort
which feels different to me than a multi-dimensional clustering algo. So for
example Cluster(a, b) might get me manifests with common tuples where A and B
are correlated but we can't actually do that here.
So for example if I would expect cluster to make files like
```
{(1,1)(1,2)(2,1)(2,2)}
{(1,3)(1,4)(2,3)(2,4)}
{(3,1)(3,2)(4,1)(4,2)}
{(3,3)(3,4)(4,3)(4,4)}
```
I would consider that clustered
But our current algo can't do that, it can only do a hierarchical sort, each
column is dependent on the one before it. Like in the above example if I
cluster (a,b) I would produce
```
{(1,1)(1,2)(1,3)(1,4)}
{(2,1)(2,2)(2,3)(2,4)}
{(3,1)(3,2)(3,3)(3,4)}
{(4,1)(4,2)(4,3)(4,4)}
```
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