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Filtering logs

Learn how to use the Filter function in LogCentral

Updated over a month ago
Filtering logs - abstract

Overview

LogCentral's filtering feature helps you reduce storage costs by automatically dropping unwanted logs before they're stored in your system.

By setting up filter patterns, you can prevent noisy, repetitive, or unnecessary log entries from consuming your storage quota—keeping only the logs that matter most to your organization.

How to Access

Navigate to your location's details page to find the Filter Rules section. You'll need appropriate permissions to manage filtering rules for your location.

Main Features

Enable/Disable Filtering

Control whether your filter rules are active with a simple toggle.

When filtering is disabled, all logs are stored as usual.

When enabled, logs matching your patterns are dropped before storage.

Pattern Management

Add regex patterns that match the logs you want to drop. The system supports:

  • Up to 50 filter patterns per location

  • Maximum 500 characters per pattern

  • Regex pattern validation with error feedback

  • Easy pattern removal when rules are no longer needed

Example Pattern

One of our customers uses this pattern in their Cisco Meraki logs to filter noise:

(pattern:\\\\s*allow all|flows allow|ip_flow_end)

Test Your Patterns

Before committing to filter rules, test them against your actual log data:

  • Preview which logs would be matched and dropped

  • See sample log lines that match your patterns

  • Test against the last 7 days of log data

  • Validate that your regex patterns work as expected

Storage Savings Preview

Make informed decisions about filtering with detailed savings information:

  • Volume reduction percentage showing what portion of logs would be filtered

  • Bytes saved displaying the actual storage impact

  • Sample matches demonstrating which log entries will be dropped

This helps you understand the cost-benefit of each filter rule before enabling it.

Regex Syntax Guide

LogCentral uses standard regex patterns to match log messages. Here's what you need to know:

Basic Syntax

  • Literal text: Matches exactly (e.g., error matches "error")

  • Dot (.): Matches any single character

  • Asterisk (*): Repeats the previous character 0 or more times

  • Plus (+): Repeats the previous character 1 or more times

  • Question mark (?): Makes the previous character optional

  • Pipe (|): OR operator (e.g., error|warning matches either)

  • Character classes: [abc] matches a, b, or c

  • Negated classes: [^abc] matches anything except a, b, or c

  • Anchors: ^ for start of message, $ for end of message

Common Patterns

  • \d - Any digit (0-9)

  • \w - Any word character (letter, digit, underscore)

  • \s - Any whitespace character

  • \b - Word boundary

  • .* - Any characters (use sparingly)

Examples

  • Drop all DEBUG logs: DEBUG

  • Drop health checks: \/health|\/ping|\/status

  • Drop specific IP: 192\.168\.1\.100 (note: escape the dots)

  • Drop a range of codes: HTTP [45]\d{2} (matches 400-599)

  • Drop multiple keywords: (test|staging|development)

Pattern Limits & Safety

To protect system performance, certain pattern types are not allowed:

Technical Limits:

  • Maximum 50 patterns per location

  • Maximum 500 characters per individual pattern

  • Maximum 10,000 characters total across all patterns

Blocked Pattern Types:

  • Excessive wildcards like .*.*.* (causes catastrophic backtracking)

  • Very large repetitions like .{1000}

  • Deeply nested groups (3+ levels)

  • Extremely long escape sequences

Important Note: Patterns are case-insensitive by default, so ERROR will match "error", "Error", and "ERROR".

How Filters Work

What Gets Matched

Filters match against the MESSAGE field of your logs - the actual log content, not metadata like timestamps or hostnames.

Multiple Pattern Logic

When you have multiple patterns:

  • A log is dropped if it matches ANY of your patterns

  • All patterns work together with OR logic

  • If a log matches pattern #1 OR pattern #2 OR pattern #3... it's dropped

Performance Tips

  • More specific patterns are faster than broad wildcards

  • Start with the most common patterns first

  • Avoid .* at the beginning of patterns when possible

  • Test patterns before enabling to ensure they work as expected

Best Practices

✅ Do:

  • Test patterns with the preview feature before enabling

  • Start with narrow, specific patterns

  • Document why each pattern exists (for team members)

  • Review filter effectiveness regularly using savings metrics

  • Keep patterns readable - break complex patterns into multiple simpler ones

❌ Don't:

  • Use overly broad patterns like .* alone

  • Filter logs you might need for debugging later

  • Enable filters without testing first

  • Create overlapping patterns (consolidate them)

  • Filter security-relevant logs

Common Use Cases

Reduce Noise from Verbose Applications
Drop debug-level logs from chatty services that generate thousands of entries per minute but provide little value in production.

Filter Out Health Checks
Eliminate repetitive health check pings from load balancers that clutter your logs without adding operational insight.

Block Spam or Bot Traffic
Remove automated scanner logs or bot requests that don't represent real user activity.

Comply with Data Policies
Drop logs containing sensitive information that shouldn't be stored, helping you meet compliance requirements.

Focus on Critical Events
Filter out informational messages to keep only warnings, errors, and critical events that require attention.

Space Savings

The filtering system provides transparent visibility into your potential storage savings. By testing patterns against recent log data, you can see exactly how much volume would be reduced before enabling filters. This data-driven approach helps you:

  • Optimize storage costs without guessing

  • Identify the highest-impact filter patterns

  • Balance between log retention and cost efficiency

  • Make confident decisions about which logs to keep

Remember that filtered logs are dropped permanently—they won't be available for search or analysis later. Choose your filter patterns carefully to ensure you're not losing valuable diagnostic information.

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