+1 (non-binding) Sounds great! Cheers, Gianluca
On Wed, 21 Oct 2026, 16:00 Junwang Zhao, <[email protected]> wrote: > On Wed, Oct 21, 2026 at 3:12 PM Yuya Ebihara > <[email protected]> wrote: > > > > Hi everyone, > > > > I opened a PR to add a standard HyperLogLog (HLL) blob type to the > Puffin spec and would like to hear your thoughts before it moves forward. > > > > PR: https://github.com/apache/iceberg/pull/18513 > > Issue: https://github.com/apache/iceberg/issues/18516 > > > > Motivation > > Puffin currently defines only one blob type for NDV statistics, > apache-datasketches-theta-v1. In some workloads, Theta sketch computation > is slow. In Trino, it causes a 10-20% slowdown on inserts. Trino is > considering an HLL option (https://github.com/trinodb/trino/pull/31173). > Since the spec has no standard HLL type, that PR has to store the sketch as > an engine-specific blob type. That means other engines can’t read it. > > +1, HLL consumes less memory and faster for simple distinct count. > > > > > Proposal > > Add a new blob type, apache-datasketches-hll-v1: > > > > It holds a serialized “compact” Apache DataSketches HLL sketch. > > The sketch is built with the default seed. Individual distinct values > are fed to it using Iceberg’s single-value serialization, the same as for > the Theta type. > > The blob metadata may include an ndv property, defined the same way as > for the Theta type. > > > > Feedback on the PR or in this thread is welcome. > > > > Thanks, > > Yuya > > > > -- > Regards > Junwang Zhao >
