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Traga seu próprio cache

New Relic's Infinite Tracing Processor is an implementation of the OpenTelemetry Collector tailsamplingprocessor. In addition to upstream features, it supports scalable and durabl distributed processing by using a distributed cache for shared state storage. This documentation how to configure it

Caches suportados

The processor supports any Redis-compatible cache implementation. It has been tested and validated with Redis and Valkey in both single-instance and cluster configurations. For production deployments, we recommend using cluster mode (sharded) to ensure high availability and scalability. To enable distributed caching, add the distributed_cache configuration to your tail_sampling processor section:

tail_sampling:
distributed_cache:
connection:
address: redis://localhost:6379/0
password: 'local'
trace_window_expiration: 30s # Default: how long to wait after last span before evaluating
processor_name: "itc" # Nane of the processor
data_compression:
format: lz4 # Optional: compression format (none, snappy, zstd, lz4); lz4 recommended

Importante

Configuration behavior: When distributed_cache is configured, the processor automatically uses the distributed cache for state management. If distributed_cache is omitted entirely, the collector will use in-memory processing instead.

O parâmetro address deve especificar um endereço de servidor válido e compatível com o Redis, usando o formato padrão:

bash
redis[s]://[[username][:password]@][host][:port][/db-number]

Alternativamente, você pode incorporar as credenciais diretamente no parâmetro address :

tail_sampling:
distributed_cache:
connection:
address: redis://:yourpassword@localhost:6379/0

O processador é implementado em Go e utiliza a biblioteca cliente go-redis.

Parâmetro de configuração

A seção distributed_cache suporta o seguinte parâmetro:

Connection settings

ParâmetroTipoPadrãoDescrição
connection.addresscordaobrigatórioRedis connection string (format: redis://host:port/db). For cluster mode, use comma-separated addresses (e.g., redis://node1:6379,redis://node2:6379)
connection.passwordcorda""Redis password for authentication

Redis client timeouts and connection pool

All settings are optional and have defaults aligned with the 10s ingestion_response_timeout.

ParâmetroTipoPadrãoDescrição
connection.dial_timeoutduration2sTimeout for establishing new connections to Redis
connection.read_timeoutduration500msTimeout for socket reads. Commands fail with timeout error if exceeded
connection.write_timeoutduration500msTimeout for socket writes. Commands fail with timeout error if exceeded
connection.pool_timeoutduration3sTime to wait for connection from pool if all connections are busy
connection.pool_sizeint20Maximum number of socket connections per Redis node
connection.min_idle_connsint5Minimum number of idle connections to maintain for quick reuse
connection.max_idle_connsint10Maximum number of idle connections to keep open
connection.conn_max_idle_timeduration1mMaximum time a connection may be idle before being closed
connection.conn_max_lifetimeduration30mMaximum time a connection may be reused before being closed
connection.max_retriesint3Maximum number of command retries before giving up
connection.min_retry_backoffduration100msMinimum backoff between retries
connection.max_retry_backoffduration1.5sMaximum backoff between retries (exponential backoff capped at this value)
connection.max_redirectsint5Maximum number of redirects to follow in cluster mode

Timeout alignment:

The default Redis client timeouts are aligned with the ingestion_response_timeout (default: 10s) to ensure Redis operations complete before workers timeout:

  • Worst case calculation: PoolTimeout(3s) + Operation(0.5s) + 3 retries × (0.5s + backoff) ≈ 7s less than 10s

Tuning guidelines:

  • High-latency Redis (cross-region, VPN): Increase timeouts to 2-3x defaults (e.g., 1-1.5s read/write) and reduce max_retries to 2
  • Very fast Redis (same host/rack): Can reduce timeouts further (e.g., 250ms) for faster failure detection
  • High throughput: Increase pool_size to 30-50 to avoid connection pool exhaustion
  • Unreliable network: Increase max_retries to 5-7 and adjust backoff settings

Cluster replica options

The connection.replica section controls cluster replica routing (cluster mode only).

ParâmetroTipoPadrãoDescrição
connection.replica.read_only_replicasbooltrueEnable routing read commands to replica nodes. Default is true for improved scalability. Set to false if strong read consistency is required.
connection.replica.route_by_latencyboolfalseRoute commands to the closest node based on latency (automatically enables read_only_replicas)
connection.replica.route_randomlyboolfalseRoute commands to a random node (automatically enables read_only_replicas)

Dica

Replica read benefits: When running with a Redis cluster that has replica nodes, enabling replica reads distributes read load across both primary and replica nodes, significantly improving read throughput (2-3x) and reducing load on primary nodes.

Important considerations:

  • Replication lag: Replicas may lag behind the primary by milliseconds to seconds
  • Cluster-only: These options only work with Redis cluster deployments
  • Read operations (Get, LRange) may be served by replica nodes
  • Write operations (SetNX, Del, Lua scripts) always route to primary nodes

Data compression

ParâmetroTipoPadrãoDescrição
data_compressioncordanoneCompression algorithm for trace data. Options: none, snappy, zstd, lz4

Dica

Compression tradeoffs:

  • none: No CPU overhead, highest Redis memory usage

  • snappy: Fast compression/decompression, good compression ratio

  • zstd: Best compression ratio, more CPU usage

  • lz4: Very fast, moderate compression ratio

    Escolha com base no seu gargalo: largura de banda da rede e armazenamento Redis versus disponibilidade do processador (CPU).

Trace management

ParâmetroTipoPadrãoDescrição
trace_window_expirationduration30sHow long to wait for spans before evaluating a trace
traces_ttlduration5mTime-to-live for trace data in Redis
cache_ttlduration30mTime-to-live for sampling decisions
processor_namecorda""Optional processor name for Redis keys and metrics (useful for multi-tenant deployments)

TTL guidelines:

  • traces_ttl should be long enough to handle retries and late spans
  • cache_ttl should be much longer than traces_ttl to handle late-arriving spans
  • Longer cache_ttl reduces duplicate evaluations but increases Redis memory usage

Retry and recovery

ParâmetroTipoPadrãoDescrição
max_retriesint2Maximum retry attempts for failed trace evaluations
in_flight_timeoutdurationSame as trace_window_expirationTimeout for in-flight batch processing before considered orphaned
recover_intervalduration5sHow often to check for orphaned batches

Importante

Orphan recovery: Orphaned batches occur when a collector crashes mid-evaluation. The orphan recovery process re-queues these traces for evaluation by another collector instance.

Evaluation settings

ParâmetroTipoPadrãoDescrição
evaluation_intervalduration1sHow often to check for traces ready for evaluation
max_traces_per_batchint1000Maximum number of traces to evaluate per batch
rate_limiterboolfalseEnable blocking rate limiter for concurrent trace processing

Rate limiter:

The rate_limiter option controls backpressure behavior when the concurrent trace limit (num_traces) is reached:

  • false (default): No rate limiting. The processor accepts traces without blocking, relying on Redis for storage. This is the recommended setting for most Redis deployments.
  • true: Enables a blocking rate limiter that applies backpressure when num_traces concurrent traces are being processed. New traces will block until a slot becomes available.

When to enable:

  • High-memory environments where you want strict control over concurrent trace processing
  • When Redis memory is constrained and you need to limit the rate of trace ingestion
  • To prevent overwhelming downstream consumers with sudden traffic bursts

Partitioning

ParâmetroTipoPadrãoDescrição
partitionsint6Number of partitions for load distribution across Redis
partition_workersint6Number of concurrent evaluation workers
partition_buffer_max_tracesint10000Maximum traces buffered per partition before flushing (2 workers per partition process in parallel)

Partitioning benefits:

  • Distributes load across multiple Redis key ranges

  • Enables parallel evaluation across multiple workers

  • Improves throughput in multi-collector deployments

    Dica

    Partition scaling: A partition is a logical shard of trace data in Redis that enables parallel processing and horizontal scaling. Traces are assigned to partitions using consistent hashing on the trace ID. Each partition can be processed independently and concurrently, enabling both vertical scaling (more CPU cores) and horizontal scaling (more collector instances).

    Important: partitions should be at least 3x times the number of Redis nodes needed for your workload. partition_workers should typically be less than or equal to the number of partitions.

Ingestion settings

ParâmetroTipoPadrãoDescrição
ingestion_workersint6Number of goroutines processing traces from the shared ingestion channel
ingestion_buffer_sizeint10000Capacity of the shared ingestion channel for buffering incoming traces
ingestion_channel_timeoutduration500msMaximum time to wait when sending traces to the ingestion channel. If exceeded, traces are dropped
ingestion_response_timeoutduration10sMaximum time to wait for a worker to process and respond. Prevents indefinite blocking if workers are stuck
hashing_strategycordarendezvousHashing algorithm for partition selection. Options: rendezvous (recommended, 3x faster) or consistent

Ingestion architecture:

The processor uses a shared channel with configurable workers for trace ingestion:

  1. Incoming traces are sent to a shared buffered channel
  2. Multiple workers pull from the channel and route traces to appropriate partitions
  3. Workers hash trace IDs using the configured hashing strategy to determine partition assignment

Configuration guidelines:

  • Buffer Size: Should absorb traffic bursts. Recommended: 10k-60k traces

  • Workers: Number of concurrent goroutines processing traces. Typically 1-2 workers per partition is optimal

  • Channel Timeout: How long to wait if buffer is full. Short timeout (500ms) fails fast on saturation

  • Response Timeout: Protects against stuck workers. Default: 10s is appropriate for normal Redis operations

  • Hashing Strategy: Algorithm for determining trace partition assignment

    • rendezvous (default): Provides superior load distribution for 2-99 partitions. Best choice for typical deployments.
    • consistent: Maintains performance when using 100+ partitions where rendezvous becomes slow. Trades slightly less optimal load distribution for better performance at scale.
    • Both strategies ensure the same trace always maps to the same partition (deterministic)
    • Choose rendezvous for better load distribution (up to 99 partitions), consistent for performance at scale (100+)

Core configuration (applies to Redis mode)

ParâmetroTipoPadrãoDescrição
num_tracesint50000Maximum concurrent processing traces
policiesmatrizobrigatórioSampling policy definitions

Complete configuration example

processors:
tail_sampling:
num_traces: 5_000_000
distributed_cache:
# Connection
connection:
address: "redis://redis-cluster:6379/0"
password: "your-redis-password"
# Connection pool settings (optional - tune for your environment)
pool_size: 30
read_timeout: 2s
write_timeout: 2s
pool_timeout: 5s
max_retries: 5
# Replica read options (cluster mode only)
replica:
read_only_replicas: true # Default: enabled for improved scalability
route_by_latency: true # Route to closest node (recommended)
# Compression
data_compression: snappy
# Trace Management
trace_window_expiration: 30s
traces_ttl: 2m # 120s (allow extra time for retries)
cache_ttl: 1h # 3600s (keep decisions longer)
processor_name: "prod-cluster-1"
# Retry and Recovery
max_retries: 3
in_flight_timeout: 45s
recover_interval: 10s
# Evaluation
evaluation_interval: 1s
max_traces_per_batch: 10000
rate_limiter: false # Recommended for Redis mode
# Partitioning
partitions: 8
partition_workers: 8
partition_buffer_max_traces: 1000
# Ingestion
ingestion_workers: 12 # 1.5 workers per partition
ingestion_buffer_size: 40000 # 40k trace buffer
ingestion_channel_timeout: 500ms
ingestion_response_timeout: 10s
hashing_strategy: rendezvous # default, best for less than 100 partitions
# Sampling policies
policies:
- name: errors
type: status_code
status_code: {status_codes: [ERROR]}
- name: slow-traces
type: latency
latency: {threshold_ms: 1000}
- name: sample-10-percent
type: probabilistic
probabilistic: {sampling_percentage: 10}

Trace evaluation

This section covers the parameters that control when traces are evaluated and how long data persists in Redis.

Evaluation timing and frequency

These parameters control when and how often the processor evaluates traces for sampling decisions:

ParâmetroTipoPadrãoDescrição
evaluation_intervalduration1sHow often to check for traces ready for evaluation
max_traces_per_batchint1000Maximum number of traces to evaluate per batch
partition_workersint6Number of concurrent evaluation workers processing partitions

How evaluation works:

  1. Every evaluation_interval, workers check for traces that have been idle for at least trace_window_expiration
  2. Up to max_traces_per_batch traces are pulled from Redis per evaluation cycle
  3. partition_workers evaluate batches concurrently across partitions

Tuning guidance:

  • Faster decisions: Decrease evaluation_interval (e.g., 500ms) for lower latency, but increases Redis load
  • Higher throughput: Increase max_traces_per_batch (e.g., 5000-10000) to process more traces per cycle
  • More parallelism: Increase partition_workers to match available CPU cores

TTL e expiração

The processor uses multiple TTL layers that work together to ensure traces are properly evaluated while managing Redis memory efficiently.

How TTL works in distributed mode

When using distributed_cache, the processor implements a multi-stage TTL system that differs from the in-memory processor:

Trace lifecycle stages:

  1. Collection phase: Spans arrive and are stored in Redis
  2. Evaluation phase: After trace_window_expiration, the trace is ready for sampling decision
  3. Retention phase: Trace data persists for traces_ttl to handle retries and late spans
  4. Cache phase: Sampling decisions persist for cache_ttl to prevent duplicate evaluations

Importante

Key difference from in-memory mode: The trace_window_expiration parameter replaces decision_wait and implements a sliding window approach:

  • Each time new spans arrive for a trace, the evaluation timer resets
  • Traces with ongoing activity stay active longer than traces that have stopped receiving spans
  • This dynamic behavior better handles real-world span arrival patterns

Why cascading TTLs matter:

The TTL hierarchy ensures data availability throughout the trace lifecycle:

  • cache_ttl (longest) handles late-arriving spans hours after evaluation
  • traces_ttl (medium) provides buffer for retries and orphan recovery
  • trace_window_expiration (shortest) controls when evaluation begins

Properly configured TTLs prevent data loss, duplicate evaluations, and incomplete traces while optimizing Redis memory usage.

Dica

Configuration principle: Each TTL should be significantly longer than the one before it (typically 5-10x). This creates safety buffers that account for processing delays, retries, and late-arriving data.

Hierarquia TTL e valores padrão

The processor uses a cascading TTL structure where each layer provides protection and buffer time for the layer below. Understanding these relationships is critical for reliable operation:

trace_window_expiration (30s)
↓ [trace ready for evaluation]
in_flight_timeout (30s default)
↓ [evaluation completes or times out]
traces_ttl (5m)
↓ [trace data deleted from Redis]
cache_ttl (30m)
↓ [decision expires, late spans re-evaluated]
1. Trace collection window: trace_window_expiration

Default: 30s | Config: distributed_cache.trace_window_expiration

  • Purpose: Controls when a trace is ready for sampling evaluation
  • Behavior: Sliding window that resets each time new spans arrive for a trace
  • Example: If a trace receives spans at t=0s, t=15s, and t=28s, evaluation begins at t=58s (28s + 30s window)

Tuning guidance:

  • Shorter values (15-20s): Faster sampling decisions, but risk of incomplete traces if spans arrive slowly
  • Longer values (45-60s): More complete traces, but higher latency and memory usage
  • Typical range: 20-45 seconds depending on your span arrival patterns
2. Batch processing timeout: in_flight_timeout

Default: Same as trace_window_expiration | Config: distributed_cache.in_flight_timeout

  • Purpose: Maximum time a batch can be in processing before being considered orphaned
  • Behavior: Prevents data loss if a collector crashes during evaluation
  • Orphan recovery: Batches exceeding this timeout are automatically re-queued for evaluation by another collector

Tuning guidance:

  • Should be ≥ trace_window_expiration: Ensures enough time for normal evaluation

  • Increase if: Your evaluation policies are computationally expensive (complex OTTL, regex)

  • Monitor: otelcol_processor_tail_sampling_sampling_decision_timer_latency to ensure evaluations complete within this window

    Dica

    Relationship with trace_window_expiration: Setting in_flight_timeout equal to trace_window_expiration works well for most deployments. Only increase if you observe frequent orphaned batch recoveries due to slow policy evaluation.

3. Trace data retention: traces_ttl

Default: 5m | Config: distributed_cache.traces_ttl

  • Purpose: How long trace span data persists in Redis after initial storage
  • Behavior: Provides buffer time for retries, late spans, and orphan recovery
  • Critical constraint: Must be significantly longer than trace_window_expiration + in_flight_timeout

Recommended formula:

traces_ttl ≥ (trace_window_expiration + in_flight_timeout + max_retries × evaluation_interval) × 2

Example with defaults:

traces_ttl ≥ (30s + 30s + 2 retries × 1s) × 2 = 124s ≈ 5m ✅

Tuning guidance:

  • Memory-constrained: Use shorter TTL (2-3m) but risk losing data for very late spans

  • Late span tolerance: Use longer TTL (10-15m) to handle delayed span arrivals

  • Standard production: 5-10 minutes provides good balance

    Importante

    Too short = data loss: If traces_ttl is too short, traces may be deleted before evaluation completes, especially during retries or orphan recovery. This results in partial or missing traces.

4. Decision cache retention: cache_ttl

Default: 30m | Config: distributed_cache.cache_ttl

  • Purpose: How long sampling decisions (sampled/not-sampled) are cached
  • Behavior: Prevents duplicate evaluation when late spans arrive after trace has been evaluated
  • Critical constraint: Must be much longer than traces_ttl

Recommended formula:

cache_ttl ≥ traces_ttl × 6

Why much longer?

  • Late-arriving spans can arrive minutes or hours after the trace completed
  • Decision cache prevents re-evaluating traces when very late spans arrive
  • Without cached decision, late spans would be evaluated as incomplete traces (incorrect sampling decision)

Tuning guidance:

  • Standard production: 30m-2h balances memory usage and late span handling
  • High late-span rate: 2-4h ensures decisions persist for very delayed data
  • Memory-constrained: 15-30m minimum, but expect more duplicate evaluations

Memory impact:

  • Each decision: ~50 bytes per trace ID

  • At 10,000 spans/sec with 20 spans/trace → 500 traces/sec

  • 30-minute cache: ~900,000 decisions × 50 bytes = ~45 MB

  • 2-hour cache: ~3.6M decisions × 50 bytes = ~180 MB

    Dica

    Monitor cache effectiveness: Track otelcol_processor_tail_sampling_early_releases_from_cache_decision metric. High values indicate the cache is preventing duplicate evaluations effectively.

TTL configuration examples

Low-latency, memory-constrained:

distributed_cache:
trace_window_expiration: 20s
in_flight_timeout: 20s
traces_ttl: 2m
cache_ttl: 15m
evaluation_interval: 500ms
max_traces_per_batch: 2000

High-throughput, late-span tolerant:

distributed_cache:
trace_window_expiration: 45s
in_flight_timeout: 60s
traces_ttl: 10m
cache_ttl: 2h
evaluation_interval: 1s
max_traces_per_batch: 10000

Balanced production (recommended):

distributed_cache:
trace_window_expiration: 30s
in_flight_timeout: 45s # Extra buffer for complex policies
traces_ttl: 5m
cache_ttl: 30m
evaluation_interval: 1s
max_traces_per_batch: 5000

Retry and recovery

ParâmetroTipoPadrãoDescrição
max_retriesint2Maximum retry attempts for failed trace evaluations
recover_intervalduration5sHow often to check for orphaned batches

Orphan recovery:

Orphaned batches occur when a collector crashes mid-evaluation. The orphan recovery process runs every recover_interval and:

  1. Identifies batches that have exceeded in_flight_timeout
  2. Re-queues these traces for evaluation by another collector instance
  3. Ensures no traces are lost due to collector failures

Tuning guidance:

  • Increase max_retries (3-5) if experiencing transient Redis errors
  • Decrease recover_interval (2-3s) for faster recovery in high-availability environments
  • Monitor recovery metrics to identify if collectors are crashing frequently

Partitioning and scaling

Partitions are the key to achieving high throughput and horizontal scalability in Redis-based tail sampling. This section explains how partitions work and how to configure them for optimal performance.

What is a partition?

A partition is a logical shard of trace data in Redis that enables parallel processing and horizontal scaling. Think of partitions as separate queues where traces are distributed based on their trace ID.

Conceitos-chave:

  • Each partition maintains its own pending traces queue in Redis

  • Traces are assigned to partitions using a configurable hashing strategy (rendezvous or consistent) on the trace ID

  • Each partition can be processed independently and concurrently

  • Partitions enable both vertical scaling (more CPU cores) and horizontal scaling (more collector instances)

    Cuidado

    Important: Changing the number of partitions when there's a cluster already running will cause data loss, since traces cannot be located anymore with a different partition count.

How partitioning works

Incoming Traces
|
v
┌─────────────────────────────┐
│ Hashing Strategy │ trace_id → rendezvous or consistent hash
│ (rendezvous by default) │
└─────────────────────────────┘
|
├──────────┬──────────┬──────────┐
v v v v
┌─────────┐ ┌─────────┐ ┌─────────┐ ┌─────────┐
│Partition│ │Partition│ │Partition│ │Partition│
│ 0 │ │ 1 │ │ 2 │ │ 3 │
│ (Redis) │ │ (Redis) │ │ (Redis) │ │ (Redis) │
└─────────┘ └─────────┘ └─────────┘ └─────────┘
| | | |
v v v v
┌─────────┐ ┌─────────┐ ┌─────────┐ ┌─────────┐
│ Worker │ │ Worker │ │ Worker │ │ Worker │
│ 0 │ │ 1 │ │ 2 │ │ 3 │
│(Goroutine)│(Goroutine)│(Goroutine)│(Goroutine)│
└─────────┘ └─────────┘ └─────────┘ └─────────┘
| | | |
└──────────┴──────────┴──────────┘
|
v
Sampled Traces

Flow:

  1. Ingestion: Trace ID is hashed using the configured hashing strategy to determine partition assignment
  2. Storage: Trace data stored in Redis under partition-specific keys
  3. Evaluation: Worker assigned to that partition pulls and evaluates traces
  4. Concurrency: All partition workers run in parallel, processing different traces simultaneously

Hashing strategy

The processor supports two hashing algorithms for partition selection. The choice depends on the number of partitions:

StrategyLoad DistributiondesempenhoBest For
rendezvous (default)Superior load balancingFast for up to 99 partitionsStandard deployments (2-99 partitions) - best load distribution for typical production workloads
consistentGood distributionMaintains performance with 100+ partitionsVery large scale (100+ partitions) - preserves performance when rendezvous becomes slow

Key characteristics:

  • Both strategies are deterministic - the same trace always maps to the same partition
  • Rendezvous provides better load distribution but becomes slow with 100+ partitions
  • Consistent hashing maintains performance at high partition counts (100+)
  • Choose based on partition count: rendezvous for better distribution (2-99), consistent for performance at scale (100+)

Standard configuration (most deployments):

distributed_cache:
hashing_strategy: rendezvous # default, best load distribution for 2-99 partitions
partitions: 8

Very large scale configuration (100+ partitions):

distributed_cache:
hashing_strategy: consistent # maintains performance with 100+ partitions
partitions: 200

Importante

Choosing the right strategy:

  • Rendezvous (default): Use for deployments with up to 99 partitions. Provides superior load distribution for the vast majority of production workloads.
  • Consistent: Use when scaling to 100+ partitions where rendezvous becomes slow. Trades slightly less optimal distribution for maintained performance at scale.
  • Important: Once chosen, changing strategies requires clearing existing data as traces will map to different partitions.

Partition configuration parameters

Use partitions to control how many logical shards you have and partition_workers to set how many workers process them:

distributed_cache:
partitions: 8 # Number of logical shards in Redis
partition_workers: 8 # Number of workers processing partitions

Worker behavior:

  • 8 partitions + 8 workers: Each worker processes one partition every evaluation_interval ✅ Balanced
  • 8 partitions + 16 workers: Each partition evaluated twice per interval (redundant, wastes resources)
  • 8 partitions + 4 workers: Only half the partitions evaluated per interval (slower, but less CPU/Redis load)

Dica

Tuning tip: Setting fewer workers per instance (partition_workers < partitions) reduces stress on Redis and the collector, useful when running many collector instances.

Partition sizing guidelines

CenárioPartitionsPartition WorkersReasoning
Desenvolvimento2-42-4Minimal overhead, easy debugging
Standard Production (15k spans/sec)4-84-8Balanced parallelism and Redis key count
High Volume (moe than 100k spans/sec)12-2412-24Maximize throughput

Importante

Important sizing rules:

  • partitions should be at least 3x the number of Redis nodes needed for your workload
  • partition_workers should typically be partitions
  • Changing partition count loses existing data - traces cannot be located after partition count changes

Partition configuration examples

Single collector (4-core machine):

distributed_cache:
partitions: 4
partition_workers: 4
partition_buffer_max_traces: 5000

Multi-collector (3 instances, 8-core each):

distributed_cache:
partitions: 12 # 3x more than single collector
partition_workers: 6 # Each collector processes 6 partitions
partition_buffer_max_traces: 10000

High-volume (10+ collectors):

distributed_cache:
partitions: 24
partition_workers: 4 # Fewer per collector to share load
partition_buffer_max_traces: 20000

Dimensionamento e desempenho

Cuidado

Critical bottlenecks: Redis performance for tail sampling is primarily constrained by CPU and network, not memory. Focus your sizing and optimization efforts on:

  1. Network throughput and latency between collectors and Redis
  2. CPU capacity for compression/decompression and Lua script execution
  3. Memory capacity (typically sufficient if CPU and network are properly sized)

Proper Redis instance sizing requires understanding your workload characteristics:

  • Spans per second: Example assumes 10,000 spans/sec throughput
  • Average span size: Example assumes 900 bytes (marshaled protobuf format)

1. CPU requirements

CPU is the primary bottleneck for Redis in tail sampling workloads due to:

Compression/decompression overhead:

  • Every span is compressed before storage and decompressed on retrieval
  • snappy or lz4: ~5-15% CPU overhead per operation
  • zstd: ~15-30% CPU overhead (higher compression ratio but more CPU intensive)
  • For 10,000 spans/sec, expect 1-2 CPU cores dedicated to compression alone

Lua script execution:

  • Atomic batch operations use Lua scripts for consistency
  • Scripts execute on a single Redis core (Redis is single-threaded per operation)
  • High evaluation rates can saturate a single core
  • Recommendation: Use Redis cluster mode to distribute Lua execution across multiple nodes

CPU sizing guidelines:

  • Single Redis instance: Minimum 4 vCPUs for 10,000 spans/sec with compression

  • Redis cluster: 3+ nodes with 4 vCPUs each for high availability and load distribution

  • Without compression: Reduce CPU requirements by ~30-40% but increase network and memory needs

    Dica

    Monitoring CPU: Watch for CPU saturation (more than 80% utilization) as the first indicator of scaling needs. If CPU-bound, either add cluster nodes or reduce compression overhead.

2. Network requirements

Network bandwidth and latency directly impact sampling throughput:

Bandwidth calculations:

For 10,000 spans/sec at 900 bytes per span:

  • Ingestion traffic (collectors → Redis): 10,000 × 900 bytes = 9 MB/sec = ~72 Mbps
  • Evaluation traffic (Redis → collectors): ~9 MB/sec = ~72 Mbps (reading traces for evaluation)
  • Total bidirectional: ~18 MB/sec = ~144 Mbps

With 25% compression (snappy/lz4):

  • Compressed traffic: ~108 Mbps bidirectional

Network sizing guidelines:

  • Co-located (same datacenter/VPC): 1 Gbps network interfaces are sufficient for most workloads

  • Cross-region: Expect 10-50ms latency - increase timeouts and use compression to reduce bandwidth

  • Connection pooling: Default pool_size: 20 supports ~5,000-10,000 spans/sec. Increase to 30-50 for higher throughput

    Importante

    Network is critical: Round-trip time between collectors and Redis directly impacts end-to-end sampling latency. Deploy Redis with low-latency network connectivity (less than 5ms) to collectors. Use cluster mode with replica reads to distribute network load.

3. Memory requirements

While memory is less constrained than CPU and network, proper sizing prevents evictions and ensures data availability.

Fórmula de estimativa de memória

Total Memory = (Trace Data) + (Decision Caches) + (Overhead)

Trace data storage

Os dados de rastreamento são armazenados no Redis durante todo o período traces_ttl para suportar intervalos que chegam com atraso e recuperação trace :

  • Armazenamento por intervalo: ~900 bytes (protobuf serializado)

  • Duração do armazenamento: Controlada por traces_ttl (padrão: 1 hora)

  • Janela de coleta ativa: Controlada por trace_window_expiration (padrão: 30s)

  • Fórmula: Memory ≈ spans_per_second × traces_ttl × 900 bytes

    Importante

    Janela ativa vs. retenção total: os traços são coletados durante uma janela ativa ~30-second (trace_window_expiration), mas persistem no Redis durante todo o período de 1 hora traces_ttl. Isso permite que o processador lide com intervalos que chegam com atraso e recupere traços órfãos. O dimensionamento do seu Redis deve levar em consideração todo o período de retenção, e não apenas a janela ativa.

Exemplo de cálculo: A 10.000 vãos/segundo com 1 hora traces_ttl:

10,000 spans/sec × 3600 sec × 900 bytes = 32.4 GB

Com compressão lz4 (observamos uma redução de 25%):

32.4 GB × 0.75 = 24.3 GB

Nota: Este cálculo representa o principal consumidor de memória. O consumo real de memória do Redis pode ser ligeiramente maior devido aos caches de decisão e às estruturas de dados internas.

Decision cache storage

Ao usar distributed_cache, os caches de decisão são armazenados no Redis sem limites de tamanho explícitos. Em vez disso, o Redis usa sua política de remoção LRU nativa (configurada via maxmemory-policy) para gerenciar a memória. Cada ID trace requer aproximadamente 50 bytes de armazenamento:

  • Cache amostrado: gerenciado pelo Redis com remoção LRU.

  • Cache não amostrado: gerenciado pelo processo de remoção LRU do Redis.

  • Sobrecarga típica por ID trace : ~50 bytes

    Dica

    gerenciamento de memória: Configure Redis com maxmemory-policy allkeys-lru para permitir a remoção automática de entradas antigas do cache de decisão quando os limites de memória forem atingidos. As chaves do cache de decisão usam expiração baseada em TTL (controlada por cache_ttl) em vez de limites de tamanho fixos.

Batch processing overhead

  • Fila de lotes atual: Mínima (IDs trace + pontuações no conjunto ordenado)
  • Lotes a bordo: max_traces_per_batch × average_spans_per_trace × 900 bytes

Exemplo de cálculo: 500 traços por lote (padrão) com 20 intervalos por trace em média:

500 × 20 × 900 bytes = 9 MB per batch

O tamanho do lote influencia o uso de memória durante a avaliação. A memória de processamento em lote durante o voo é temporária e liberada após a conclusão do processamento.

Exemplo completo de dimensionamento

Workload parameters:

  • Taxas de transferência: 10.000 spans/segundo
  • Tamanho médio do intervalo: 900 bytes
  • Período de armazenamento: 1 hora (traces_ttl)
  • Deployment: Redis cluster with 3 nodes

Resource requirements:

RecursoWithout CompressionWith lz4 Compression (25% reduction)
CPU per node2-3 vCPUs3-4 vCPUs (compression overhead)
Network bandwidth~144 Mbps bidirectional~108 Mbps bidirectional
Memory (total)~40.5 GB + decision cache~30.4 GB + decision cache

Memory breakdown with compression:

Componentememória necessária
dados de rastreamento (retenção de 1 hora)24,3 GB
Caches de decisãoVariável (gerenciada por LRU)
Processamento em lote~7 MB
Sobrecarga do Redis (25%)~6.1 GB
Total (mínimo)~30.4 GB + decision cache

Recommended Redis cluster configuration:

# 3-node Redis cluster (e.g., AWS cache.r6g.xlarge)
Nodes: 3
vCPUs per node: 4
Memory per node: 25 GB (75 GB total cluster)
Network: 1 Gbps or better
Region: Co-located with collectors (5ms latency)

Importante

Sizing guidance:

  • CPU-first approach: Size for CPU requirements first, then verify memory and network adequacy
  • Cluster mode strongly recommended: Distributes CPU, network, and memory load across nodes
  • Monitoring: Track CPU utilization, network throughput, and memory usage to identify bottlenecks
  • Scaling: If CPU-bound (more than 70% utilization), add cluster nodes. If network-bound, enable compression or add nodes
  • Buffer for spikes: Provision 20-30% additional capacity beyond steady-state requirements

Default configuration architecture

The default configuration values are designed for a reference deployment supporting 1 million spans per minute (~16,000 spans/sec):

Collector deployment:

  • 3 collector instances
  • 4 vCPUs per instance
  • 8 GB RAM per instance

Redis cluster:

  • 3 Redis instances (AWS cache.r6g.xlarge: 4 vCPUs, 25.01 GiB memory each)
  • Configured as a cluster for high availability and load distribution
  • Co-located with collectors for low-latency access

This reference architecture provides a starting point for production deployments. Adjust based on your actual throughput and latency requirements.

Metrics reference

The tail sampling processor emits the following metrics in Redis-distributed mode to help you monitor performance and diagnose issues.

Métricas disponíveis

Nome da métricaDimensõesDescriçãoUse Case
otelcol_processor_tail_sampling_batchespartition, processorNumber of batch operationsMonitor batch processing rate across partitions
otelcol_processor_tail_sampling_sampling_decision_timer_latencypartition, processorSampling decision timer latency (ms)Track overall evaluation performance per partition
otelcol_processor_tail_sampling_sampling_policy_evaluation_errorpartition, processorPolicy evaluation error countDetect policy configuration issues
otelcol_processor_tail_sampling_count_traces_sampledpolicy, decision, partition, processorCount of traces sampled/not sampled per policyTrack per-policy sampling decisions
otelcol_processor_tail_sampling_count_spans_sampledpolicy, decision, partition, processorCount of spans sampled/not sampled per policySpan-level sampling statistics
otelcol_processor_tail_sampling_global_count_traces_sampleddecision, partition, processorGlobal count of traces sampled by at least one policyOverall sampling rate monitoring
otelcol_processor_tail_sampling_early_releases_from_cache_decisionsampledSpans immediately released due to cache hitDecision cache effectiveness
otelcol_processor_tail_sampling_new_trace_id_receivedpartition, processorCount of new traces receivedTrace ingestion rate per partition
otelcol_processor_tail_sampling_new_span_receivedpartition, processorCount of new spans receivedSpan ingestion rate per partition
otelcol_processor_tail_sampling_traces_droppedpartition, processorTraces dropped due to saving errorsError detection and troubleshooting
otelcol_processor_tail_sampling_spans_droppedpartition, processorSpans dropped due to saving errorsError detection and troubleshooting
otelcol_processor_tail_sampling_count_traces_deleteddeleted, partition, processorCount of traces deleted from storageCleanup monitoring

Dimension details

  • policy: Name of the sampling policy that made the decision
  • sampled: Whether the decision was to sample (true/false)
  • decision: The sampling decision type (sampled, not_sampled, dropped)
  • deleted: Whether deletion was successful (true/false)
  • partition: Partition identifier (hex-encoded hash, e.g., {a1b2c3d4...}) - ensures Redis Cluster hash tag compatibility
  • processor: Processor instance identifier (from distributed_cache.processor_name config)

Dica

Partition identifiers: Partition values are deterministic SHA256 hashes of the partition index combined with the processor name. Check collector logs at startup to see the mapping of partition indices to hash values.

Requisitos de cache compatíveis com Redis

O processador utiliza o cache como armazenamento distribuído para os seguintes dados trace :

  • atributo de rastreamento e extensão
  • Dados trace ativos
  • Cache de decisão de amostragem

O processador executa um script Lua para interagir atomicamente com o cache Redis. O suporte script Lua geralmente está habilitado por padrão em caches compatíveis com Redis. Nenhuma configuração adicional é necessária, a menos que você tenha desativado explicitamente esse recurso.

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