Analyzer ngx-shm-slabs

# Name

ngx-shm-slabs - Slab Memory Usage in Nginx Shared Memory

This analyzer monitors slab allocator memory usage within Nginx shared memory zones in OpenResty, Kong, and Nginx applications. It captures detailed memory allocation statistics across different slab size classes (32B to 4096B) for each shared memory zone, including both free and used memory distributions. The analyzer tracks slab tree heights to detect fragmentation and generates pie charts visualizing memory distribution patterns across zones, helping identify memory waste, fragmentation issues, and optimize shared memory configuration for lua_shared_dict, proxy_cache, and other shared memory consumers.

# Resource Category

Memory.

# Application Type & Technical Stack

• OpenResty
• Nginx
• Kong
• APISIX

# Command Line Syntax

The analyzer can be invoked directly on the command-line via the orxray utility from the openresty-xray-cli software package.

Alternatively, the analyzer can also be invoked manually or automatically on the web console UI of OpenResty XRay (like on the Advanced web page).

# PID is the target process PID.
orxray analyzer run ngx-shm-slabs -p PID

# trace a shell command directly
orxray analyzer run ngx-shm-slabs -c SHELL_CMD

# Tracing Multiple Processes

Not supported.

# Output Formats

• Pie Charts
• Plain Texts

# Output Example

{
  "stats": {
    "lock": {
      "free": {"min": 32, "max": 4096, "count": 409, "sum": 1040192},
      "used": {"min": 32, "max": 128, "count": 3, "sum": 192}
    },
    "waf": {
      "free": {"min": 32, "max": 4096, "count": 2698, "sum": 10419904},
      "used": {"min": 32, "max": 128, "count": 4, "sum": 320}
    },
    "proxycache": {
      "free": {"min": 64, "max": 4096, "count": 37091, "sum": 102606400},
      "used": {"min": 64, "max": 128, "count": 12788, "sum": 1636800}
    },
    "limit_req_shdict": {
      "free": {"min": 64, "max": 4096, "count": 26957, "sum": 110036288},
      "used": {"min": 64, "max": 256, "count": 131457, "sum": 23395008}
    },
    "ssl_session_cache": {
      "free": {"min": 64, "max": 4096, "count": 17715, "sum": 64693824},
      "used": {"min": 64, "max": 512, "count": 3964, "sum": 2021824}
    }
  },
  "distributions": {
    "lock": {
      "free": {"32": 126, "128": 31, "4096": 252},
      "used": {"32": 2, "128": 1}
    },
    "proxycache": {
      "free": {"64": 63, "128": 12365, "4096": 24663},
      "used": {"64": 1, "128": 12787}
    },
    "limit_req_shdict": {
      "free": {"64": 63, "128": 21, "256": 11, "4096": 26862},
      "used": {"64": 1, "128": 80139, "256": 51317}
    }
  },
  "heights": {
    "lock": {"min": 0, "max": 0, "avg": 0},
    "waf": {"min": 1, "max": 1, "avg": 1},
    "proxycache": {"min": 12, "max": 14, "avg": 13.2},
    "limit_req_shdict": {"min": 16, "max": 19, "avg": 17}
  },
  "kind": {
    "lock": "http_lua_shdict",
    "waf": "http_lua_shdict",
    "proxycache": "http_file_cache",
    "limit_req_shdict": "http_lua_shdict"
  }
}

# Author

The OpenResty Inc. Team.

# Copyright

Copyright (C) by OpenResty Inc. All rights reserved.