Towards Optimal Moment Estimation in Streaming and Distributed Models
Pith reviewed 2026-05-24 22:13 UTC · model grok-4.3
The pith
For p in (0,1], the p-moment can be estimated to (1+ε) using Õ(ε^{-2} + log n) bits on any worst-case stream of positive updates.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
For p ∈ (0,1] we give a streaming algorithm that estimates ||X||_p^p to (1+ε) accuracy using Õ(ε^{-2} + log n) bits on worst-case streams of non-negative updates. In coordinator and blackboard topologies for p ∈ (1,2] a randomized-rounding protocol uses Õ(ε^{-2}) bits of max-communication; the bound generalizes to Õ(ε^{-2} log d) bits on any communication graph of diameter d. These protocols also solve heavy hitters and approximate matrix product.
What carries the argument
A worst-case streaming algorithm for small p that avoids the random-order assumption, together with a randomized rounding scheme that produces the communication bounds for larger p.
If this is right
- New upper bounds hold for estimating empirical entropy in a stream.
- The same protocols give communication-efficient solutions for heavy hitters and approximate matrix product.
- Natural communication-complexity reductions cannot prove an Ω(ε^{-2} log n) streaming lower bound for p in (1,2]; any such lower bound must exploit large-diameter topologies.
- The Õ(ε^{-2} log d) bound applies to arbitrary communication graphs of diameter d.
Where Pith is reading between the lines
- Techniques that succeed without random order for p ≤ 1 may extend to other streaming statistics previously analyzed only under random-order assumptions.
- The separation between p ≤ 1 and p > 1 suggests that the ordering hardness is concentrated in the regime where moments behave more like norms.
- Diameter dependence implies that network topology itself can be a resource for reducing communication in distributed moment estimation.
Load-bearing premise
All updates are non-negative and the algorithm is allowed to be randomized.
What would settle it
An explicit worst-case stream of positive updates on which every algorithm estimating ||X||_p^p for some p ≤ 1 either exceeds Õ(ε^{-2} + log n) bits or fails to return a (1+ε) approximation.
Figures
read the original abstract
One of the oldest problems in the data stream model is to approximate the $p$-th moment $\|\mathcal{X}\|_p^p = \sum_{i=1}^n |\mathcal{X}_i|^p$ of an underlying vector $\mathcal{X} \in \mathbb{R}^n$, which is presented as a sequence of poly$(n)$ updates to its coordinates. Of particular interest is when $p \in (0,2]$. Although a tight space bound of $\Theta(\epsilon^{-2} \log n)$ bits is known for this problem when both positive and negative updates are allowed, surprisingly there is still a gap in the space complexity when all updates are positive. Specifically, the upper bound is $O(\epsilon^{-2} \log n)$ bits, while the lower bound is only $\Omega(\epsilon^{-2} + \log n)$ bits. Recently, an upper bound of $\tilde{O}(\epsilon^{-2} + \log n)$ bits was obtained assuming that the updates arrive in a random order. We show that for $p \in (0, 1]$, the random order assumption is not needed. Namely, we give an upper bound for worst-case streams of $\tilde{O}(\epsilon^{-2} + \log n)$ bits for estimating $\|\mathcal{X}\|_p^p$. Our techniques also give new upper bounds for estimating the empirical entropy in a stream. On the other hand, we show that for $p \in (1,2]$, in the natural coordinator and blackboard communication topologies, there is an $\tilde{O}(\epsilon^{-2})$ bit max-communication upper bound based on a randomized rounding scheme. Our protocols also give rise to protocols for heavy hitters and approximate matrix product. We generalize our results to arbitrary communication topologies $G$, obtaining an $\tilde{O}(\epsilon^{2} \log d)$ max-communication upper bound, where $d$ is the diameter of $G$. Interestingly, our upper bound rules out natural communication complexity-based approaches for proving an $\Omega(\epsilon^{-2} \log n)$ bit lower bound for $p \in (1,2]$ for streaming algorithms. In particular, any such lower bound must come from a topology with large diameter.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript presents algorithmic results for approximating the p-th moment of a vector in streaming and distributed settings. For p ∈ (0,1], it claims an Õ(ε^{-2} + log n) bit space upper bound for worst-case positive streams, removing the need for random order. It also gives bounds for empirical entropy. For p ∈ (1,2], it provides Õ(ε^{-2}) max-communication upper bounds in coordinator and blackboard models using randomized rounding, generalizing to Õ(ε^{-2} log d) for graphs with diameter d, with applications to heavy hitters and matrix product approximation.
Significance. These results are significant because they nearly close the gap for the streaming moment estimation problem for small p and provide efficient distributed protocols. The explicit constructions and the implication ruling out certain lower bound techniques based on communication complexity are valuable contributions. The paper credits the randomized rounding technique explicitly.
major comments (1)
- [distributed models section] The randomized rounding scheme for p ∈ (1,2] in the coordinator/blackboard models is load-bearing for the Õ(ε^{-2}) max-communication claim; the error analysis must confirm that the rounding does not introduce n-dependent factors that would violate the bound (see abstract and the distributed-model section).
minor comments (2)
- [Introduction] The introduction could include a table comparing the new bounds to prior work for p ≤ 1 and p ∈ (1,2] to clarify the contribution.
- [Abstract and Section 1] Expand the definition of the tilde notation in the main text to explicitly list the hidden logarithmic factors in the space and communication bounds.
Simulated Author's Rebuttal
We thank the referee for their careful reading of the manuscript, positive assessment of the results, and recommendation for minor revision. We address the single major comment below.
read point-by-point responses
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Referee: [distributed models section] The randomized rounding scheme for p ∈ (1,2] in the coordinator/blackboard models is load-bearing for the Õ(ε^{-2}) max-communication claim; the error analysis must confirm that the rounding does not introduce n-dependent factors that would violate the bound (see abstract and the distributed-model section).
Authors: We appreciate the referee drawing attention to this aspect of the analysis. The error analysis for the randomized rounding scheme (detailed in the proof of the main theorem in the distributed-model section) already confirms that no n-dependent factors are introduced into the Õ(ε^{-2}) max-communication bound. Each update is rounded independently with probability proportional to its contribution to the current p-moment estimate; the resulting bias and variance are bounded using the p-norm properties for p ∈ (1,2], yielding an additive error of O(ε ||X||_p^p) that holds with high probability and depends only on ε and the moment value itself. The total communication therefore remains Õ(ε^{-2}) bits in both the coordinator and blackboard models, as claimed in the abstract. The current write-up already contains the necessary bounds; we do not believe a change is required. revision: no
Circularity Check
No significant circularity in derivation chain
full rationale
The paper establishes upper bounds via explicit algorithmic constructions and protocols for p-moment estimation on worst-case streams (p in (0,1]) and distributed models. These rest on randomized rounding schemes, communication topologies, and new techniques rather than self-definitional loops, fitted inputs renamed as predictions, or load-bearing self-citations. The abstract and claims describe independent results with no equations or steps that reduce by construction to the paper's own inputs or prior self-citations. This matches the default case of a self-contained theoretical construction.
Axiom & Free-Parameter Ledger
axioms (1)
- standard math Standard properties of the p-norm and the data-stream update model with non-negative updates
Lean theorems connected to this paper
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IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
We show that for p ∈ (0,1], ... upper bound ... Õ(ε^{-2} + log n) bits for estimating ||X||_p^p ... randomized rounding scheme ... p-stable sketches
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IndisputableMonolith/Foundation/RealityFromDistinction.leanreality_from_one_distinction unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
p-stable distributions ... tail behavior ... variance bound ... Morris counters
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Reference graph
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