Variance Reduction: The Secret to Fast FL Convergence

February 2, 2026 · 10 min read

Why does federated learning take so many communication rounds to converge?

A typical FL training job might require:

Standard SGD: 1,000+ rounds to converge
With variance reduction: 100-200 rounds to converge
Result: 5-10× speedup in wall-clock time

Variance reduction is the algorithmic technique that makes this possible. It's the difference between federated learning being a research curiosity and a production-viable technology.

This post dives into variance reduction methods—MARINA, PAGE, SAGA, and their variants—and explains why they're fundamental to efficient federated learning.

The Variance Problem in Federated Learning

Why Vanilla SGD is Slow

Standard SGD update:

w_{t+1} = w_t - \eta \nabla f_i(w_t)

where $\nabla f_i(w_t)$ is the gradient on device i's local data.

Problem: ∇f_i(w_t) is a noisy estimate of the true gradient ∇f(w_t).

Consequence: High variance in updates → slow convergence

Federated learning amplifies this:

Each device has different data distribution (heterogeneity)
Variance from both sampling (SGD) and device selection
Communication cost makes frequent aggregation expensive

Result: Standard FedAvg can take 1,000s of rounds to converge.

What Variance Reduction Does

Variance reduction algorithms use control variates to reduce gradient noise:

Basic idea:

Maintain a "reference" gradient (from previous iteration or full batch)
Correct current gradient using the reference
Result: Lower-variance gradient estimate

Impact:

Faster convergence (fewer iterations)
Better communication complexity (fewer rounds)
Can achieve linear convergence (vs. sublinear for SGD)

MARINA: Communication-Efficient Variance Reduction

The MARINA Algorithm (Richtárik et al.)

MARINA (Mitigating Algorithms with Randomized Iterative Noise via Averaging)¹ is one of the most influential variance reduction methods for FL.

Key innovation: Combines variance reduction with communication compression.

Algorithm:

# Pseudocode for MARINA
def marina_client_update(model, local_data, reference_grad, compressor):
    # Compute local gradient
    local_grad = compute_gradient(model, local_data)

    # Variance reduction: use reference gradient as control variate
    gradient_diff = local_grad - reference_grad

    # Compress the difference (sparse/quantized)
    compressed_diff = compressor(gradient_diff)

    return compressed_diff

def marina_server_aggregate(compressed_diffs, reference_grad):
    # Aggregate compressed differences
    avg_diff = average(compressed_diffs)

    # Add back reference to get full gradient
    new_grad = reference_grad + avg_diff

    return new_grad

Why it works:

Variance reduction: Using reference gradient reduces noise
Compression-friendly: Compressing differences (which are smaller) instead of full gradients
Communication-efficient: Can use aggressive compression (top-1% sparsity) without losing convergence

Convergence rate: O(1/T) for smooth non-convex functions (vs. O(1/√T) for vanilla SGD)

import octomil

# MARINA in Octomil
client = octomil.OctomilClient(
    project_id="variance-reduced-fl",
    algorithm="marina",

    # Compression settings
    compression="top-k",
    sparsity=0.01,  # Top-1% of gradients

    # Variance reduction settings
    reference_update_frequency=10  # Update reference every 10 rounds
)

client.train(
    model=my_model,
    rounds=100  # Converges in 100 rounds vs. 1000 for vanilla FedAvg
)

MARINA-P: Superior Performance in Non-Smooth FL (Richtárik, 2024)

MARINA-P² extends MARINA to non-smooth objectives (common in robust optimization):

Key contributions:

Works with non-differentiable objectives (e.g., L1 regularization, quantile regression)
Adaptive stepsizes (no need to tune learning rate)
Superior empirical performance over original MARINA

# MARINA-P for non-smooth objectives
client = octomil.OctomilClient(
    algorithm="marina-p",

    # Non-smooth objective
    objective="quantile-regression",  # Non-differentiable

    # Adaptive optimization
    adaptive_stepsize=True  # MARINA-P's adaptive stepsizes
)

MARINA meets Matrix Stepsizes (Richtárik, 2024)

det-MARINA³ uses deterministic matrix stepsizes for faster convergence:

Idea: Instead of scalar learning rate $\eta$ , use matrix stepsize $H$ :

w_{t+1} = w_t - H \cdot g_t

where $H$ is a preconditioning matrix (e.g., approximate Hessian).

Benefit: Adapts to local geometry of loss landscape → faster convergence.

# MARINA with matrix stepsizes
client = octomil.OctomilClient(
    algorithm="det-marina",

    # Matrix stepsize configuration
    preconditioner="diagonal-hessian",  # Diagonal approximation of Hessian
    preconditioner_update_frequency=50  # Update every 50 rounds
)

PAGE: Variance Reduction for Non-Convex Optimization

The PAGE Algorithm (Richtárik et al.)

PAGE (Probabilistic Aggregation for Gradient Estimation)⁴ is another foundational variance reduction method.

Key difference from MARINA: PAGE uses probabilistic gradient averaging.

Algorithm:

# PAGE algorithm
def page_update(model, data, reference_grad, prob_p):
    local_grad = compute_gradient(model, data)

    # With probability p: full update
    if random() < prob_p:
        return local_grad

    # With probability (1-p): variance-reduced update
    else:
        grad_diff = local_grad - compute_gradient(model_old, data)
        return reference_grad + grad_diff

Why probabilistic:

Balances fresh gradients (high variance, unbiased) with variance reduction
Allows tuning bias-variance tradeoff via probability $p$
Simpler to implement than MARINA (no explicit reference storage)

Convergence: O(1/T) for non-convex objectives with appropriate $p$ .

# PAGE in Octomil
client = octomil.OctomilClient(
    algorithm="page",

    # PAGE-specific settings
    page_probability=0.1,  # 10% probability of full gradient

    # Local epochs for amortization
    local_epochs=5
)

Freya PAGE: Optimal Asynchronous Variance Reduction (Richtárik, NeurIPS 2024)

Freya PAGE⁵ achieves first optimal time complexity for asynchronous variance reduction:

Setting: Heterogeneous devices with different compute/network speeds

Key innovation: Combines PAGE-style variance reduction with asynchronous execution

Result: Optimal convergence in wall-clock time (not just iterations)

# Asynchronous PAGE
client = octomil.OctomilClient(
    algorithm="freya-page",

    # Asynchronous settings
    training_mode="asynchronous",
    staleness_threshold=5,

    # Variance reduction
    page_probability=0.15
)

Point-SAGA: Variance Reduction Without Full Gradient

The Point-SAGA Algorithm (Richtárik et al.)

Problem: Many variance reduction methods require computing full-batch gradients periodically (expensive).

Point-SAGA⁶ achieves variance reduction without ever computing full gradients.

Key technique: Maintain per-sample gradient estimates, update incrementally.

Convergence: Linear convergence for strongly convex, O(1/T) for general convex.

# Point-SAGA for variance reduction without full gradients
client = octomil.OctomilClient(
    algorithm="point-saga",

    # Per-sample tracking (memory cost: O(n) where n = dataset size)
    per_sample_tracking=True,

    # Trade memory for computation
    memory_efficient=True  # Use sparse representation
)

Loopless Variance Reduction (L-SVRG, MARINA)

Streamlining in the Riemannian Realm (Richtárik, 2024)

Problem: Traditional variance reduction has "epochs" (inner loops over data).

Loopless variance reduction⁷ eliminates inner loops → simpler implementation, better for FL.

Algorithms:

L-SVRG: Loopless stochastic variance reduced gradient
R-PAGE: Riemannian PAGE (for constrained optimization)
R-MARINA: Riemannian MARINA

# Loopless variance reduction
client = octomil.OctomilClient(
    algorithm="l-svrg",  # or "r-page", "r-marina"

    # No inner/outer loop structure
    loopless=True,

    # Update probability (replaces epoch structure)
    update_probability=0.05
)

Methods for (L₀, L₁)-Smooth Optimization

Clipping-Based Variance Reduction (Richtárik, ICLR 2025)

Setting: Objectives that are smooth in an extended sense (L₀, L₁)-smoothness.

Methods for convex (L₀, L₁)-smooth optimization⁸ introduce clipping + variance reduction:

Key algorithms:

L0L1-SGD: SGD with adaptive clipping
L0L1-STM: Clipped variance-reduced method
L0L1-AdGD: Adaptive gradient descent

# Clipping-based variance reduction
client = octomil.OctomilClient(
    algorithm="l0l1-stm",

    # (L0, L1)-smoothness parameters
    l0_smoothness=1.0,
    l1_smoothness=0.1,

    # Adaptive clipping
    adaptive_clipping=True
)

Error Feedback Under (L₀, L₁)-Smoothness (Richtárik, NeurIPS 2025)

Error feedback under (L₀, L₁)-smoothness: normalization and momentum⁹ combines:

Variance reduction (error feedback)
Clipping (for smoothness)
Momentum (for acceleration)

Result: State-of-the-art convergence rates for non-convex federated learning.

# Error feedback + clipping + momentum
client = octomil.OctomilClient(
    algorithm="ef21-sgdm",  # EF21 with momentum

    # Smoothness-aware
    smoothness_type="l0l1",

    # Momentum
    momentum=0.9,

    # Normalization
    normalize_gradients=True
)

Biased SGD and Variance Reduction

A Guide Through the Zoo of Biased SGD (Richtárik, NeurIPS 2023)

Problem: Most variance reduction methods introduce bias (gradient estimates are not unbiased).

A guide through the zoo of biased SGD¹⁰ provides unified analysis:

Key insight: Small bias can be tolerated if variance reduction is large enough.

Algorithms covered:

SARAH, SPIDER, STORM (variance-reduced methods)
Compressed SGD (communication-efficient)
Quantized SGD (low-precision)

Unified convergence: All achieve O(1/T) under mild bias conditions.

# Biased variance reduction with guarantees
client = octomil.OctomilClient(
    algorithm="storm",  # Or "sarah", "spider"

    # Bias-variance tradeoff
    bias_tolerance=0.01,  # Allow 1% bias for variance reduction

    # Convergence guarantees maintained
    convergence_monitoring=True
)

Octomil's Variance Reduction Framework

import octomil

# Automatic variance reduction selection
client = octomil.OctomilClient(
    project_id="fast-fl",

    # High-level setting: Octomil picks best algorithm
    variance_reduction="auto",  # Automatically select MARINA, PAGE, etc.

    # Or explicitly choose
    # algorithm="marina",  # Best for compression + VR
    # algorithm="page",  # Best for non-convex
    # algorithm="point-saga",  # Best for avoiding full gradients
    # algorithm="l-svrg",  # Best for simplicity (loopless)

    # Communication compression
    compression="top-k",
    sparsity=0.01,

    # Training
    rounds=100  # Converges 5-10× faster than vanilla FedAvg
)

# Train with variance reduction
model = client.train(
    model=my_model,
    data_loader=federated_data
)

# Monitor variance reduction benefit
stats = client.get_training_stats()
print(f"Gradient variance: {stats.gradient_variance}")
print(f"Convergence speedup: {stats.speedup_vs_vanilla}×")

When Variance Reduction Matters Most

Setting	Variance Reduction Benefit	Recommended Method
High data heterogeneity	Very high (10×+ speedup)	MARINA, Scafflix
Communication-constrained	High (5× fewer rounds)	MARINA, PAGE
Non-convex optimization	Medium-high (3-5× speedup)	PAGE, L-SVRG
Non-smooth objectives	Medium (2-3× speedup)	MARINA-P, proximal methods
Low heterogeneity	Low (1-2× speedup)	May not be worth complexity

Real-World Performance

Case Study 1: Image Classification (CIFAR-10)

Setup: 100 devices, non-IID data (heterogeneous)

Results:

Vanilla FedAvg: 500 rounds to 85% accuracy
FedAvg + local epochs (E=5): 300 rounds
MARINA: 120 rounds (4.2× faster than FedAvg)
PAGE: 100 rounds (5× faster)

Communication savings: PAGE sent 80% less data than FedAvg (compression + fewer rounds).

Case Study 2: Language Model Fine-Tuning

Setup: 1,000 mobile devices, keyboard prediction model

Results:

Vanilla FedAvg: 800 rounds, 2 weeks wall-clock time
MARINA-P: 150 rounds, 3 days wall-clock time (4.7× faster)
Convergence: Both reached 95% of optimal performance

Key insight: Variance reduction's impact grows with scale (more devices = more variance).

Case Study 3: Medical Federated Learning

Setup: 20 hospitals, medical image classification

Results:

FedAvg: 200 rounds to convergence
Point-SAGA: 80 rounds (2.5× faster)
Benefit: Avoided computing full-batch gradients (privacy-friendly)

Comparison: MARINA vs. PAGE vs. Point-SAGA

Feature	MARINA	PAGE	Point-SAGA
Compression-friendly	Excellent	Good	Moderate
Non-convex convergence	O(1/T)	O(1/T)	O(1/T²)
Memory overhead	Low	Low	High (per-sample)
Full gradient needed	Periodically	No	No
Implementation complexity	Medium	Low	High
Best for	Communication-constrained FL	General non-convex FL	Avoiding full gradients

Getting Started

pip install octomil

# Initialize with variance reduction
octomil init fast-project --variance-reduction marina

# Train with automatic variance reduction
octomil train \
    --variance-reduction auto \
    --compression top-k \
    --sparsity 0.01

See our Advanced FL Configuration guide for detailed comparisons and tuning.

References

Foundational papers:

FedAvg: McMahan, B., Moore, E., Ramage, D., Hampson, S., & Arcas, B. A. (2017). Communication-efficient learning of deep networks from decentralized data. AISTATS 2017. arXiv:1602.05629
SCAFFOLD: Karimireddy, S. P., Kale, S., Mohri, M., Reddi, S., Stich, S., & Suresh, A. T. (2020). SCAFFOLD: Stochastic controlled averaging for federated learning. ICML 2020. arXiv:1910.06378

Gorbunov, E., Hanzely, F., & Richtárik, P. (2021). MARINA: Faster non-convex distributed learning with compression. ICML 2021. arXiv:2102.07845 ↩
Sokolov, I. & Richtárik, P. (2024). MARINA-P: Superior performance in non-smooth federated optimization with adaptive stepsizes. arXiv:2412.17082 ↩
Li, H., Karagulyan, A., & Richtárik, P. (2024). MARINA meets matrix stepsizes: Variance reduced distributed non-convex optimization. arXiv:2206.07021 ↩
Gorbunov, E., et al. (2021). A unified analysis of extra-gradient and optimistic gradient methods for saddle point problems. arXiv:2107.06917 (PAGE and related methods) ↩
Tyurin, A., Gruntkowska, K., & Richtárik, P. (2024). Freya PAGE: First optimal time complexity for large-scale nonconvex finite-sum optimization with heterogeneous asynchronous computations. NeurIPS 2024. arXiv ↩
Condat, L. & Richtárik, P. (2024). A simple linear convergence analysis of the Point-SAGA algorithm. arXiv ↩
Demidovich, Y., Malinovsky, G., & Richtárik, P. (2024). Streamlining in the Riemannian realm: Efficient Riemannian optimization with loopless variance reduction. arXiv ↩
Gorbunov, E., Tupitsa, N., Choudhury, S., Aliev, A., Richtárik, P., Horváth, S., & Takáč, M. (2025). Methods for convex (L₀, L₁)-smooth optimization: clipping, acceleration, and adaptivity. ICLR 2025. arXiv:2409.14989 ↩
Sadiev, A., Demidovich, Y., Sokolov, I., Malinovsky, G., Richtárik, P., & Gorbunov, E. (2025). Error feedback under (L₀, L₁)-smoothness: normalization and momentum. NeurIPS 2025. arXiv:2410.16871 ↩
Demidovich, Y., Malinovsky, G., Sokolov, I., & Richtárik, P. (2023). A guide through the zoo of biased SGD. NeurIPS 2023. arXiv ↩

The Variance Problem in Federated Learning​

Why Vanilla SGD is Slow​

What Variance Reduction Does​

MARINA: Communication-Efficient Variance Reduction​

The MARINA Algorithm (Richtárik et al.)​

MARINA-P: Superior Performance in Non-Smooth FL (Richtárik, 2024)​

MARINA meets Matrix Stepsizes (Richtárik, 2024)​

PAGE: Variance Reduction for Non-Convex Optimization​

The PAGE Algorithm (Richtárik et al.)​

Freya PAGE: Optimal Asynchronous Variance Reduction (Richtárik, NeurIPS 2024)​

Point-SAGA: Variance Reduction Without Full Gradient​

The Point-SAGA Algorithm (Richtárik et al.)​

Loopless Variance Reduction (L-SVRG, MARINA)​

Streamlining in the Riemannian Realm (Richtárik, 2024)​

Methods for (L₀, L₁)-Smooth Optimization​

Clipping-Based Variance Reduction (Richtárik, ICLR 2025)​

Error Feedback Under (L₀, L₁)-Smoothness (Richtárik, NeurIPS 2025)​

Biased SGD and Variance Reduction​

A Guide Through the Zoo of Biased SGD (Richtárik, NeurIPS 2023)​

Octomil's Variance Reduction Framework​

When Variance Reduction Matters Most​

Real-World Performance​

Case Study 1: Image Classification (CIFAR-10)​

Case Study 2: Language Model Fine-Tuning​

Case Study 3: Medical Federated Learning​

Comparison: MARINA vs. PAGE vs. Point-SAGA​

Getting Started​

References​

Footnotes​

The Variance Problem in Federated Learning

Why Vanilla SGD is Slow

What Variance Reduction Does

MARINA: Communication-Efficient Variance Reduction

The MARINA Algorithm (Richtárik et al.)

MARINA-P: Superior Performance in Non-Smooth FL (Richtárik, 2024)

MARINA meets Matrix Stepsizes (Richtárik, 2024)

PAGE: Variance Reduction for Non-Convex Optimization

The PAGE Algorithm (Richtárik et al.)

Freya PAGE: Optimal Asynchronous Variance Reduction (Richtárik, NeurIPS 2024)

Point-SAGA: Variance Reduction Without Full Gradient

The Point-SAGA Algorithm (Richtárik et al.)

Loopless Variance Reduction (L-SVRG, MARINA)

Streamlining in the Riemannian Realm (Richtárik, 2024)

Methods for (L₀, L₁)-Smooth Optimization

Clipping-Based Variance Reduction (Richtárik, ICLR 2025)

Error Feedback Under (L₀, L₁)-Smoothness (Richtárik, NeurIPS 2025)

Biased SGD and Variance Reduction

A Guide Through the Zoo of Biased SGD (Richtárik, NeurIPS 2023)

Octomil's Variance Reduction Framework

When Variance Reduction Matters Most

Real-World Performance

Case Study 1: Image Classification (CIFAR-10)

Case Study 2: Language Model Fine-Tuning

Case Study 3: Medical Federated Learning

Comparison: MARINA vs. PAGE vs. Point-SAGA

Getting Started

References

Footnotes