managing-memcached

name	managing-memcached
description	Use when working with Memcached — memcached instance monitoring, slab allocation analysis, hit ratio optimization, and connection management. Covers memory utilization, eviction rates, item distribution across slabs, connection pool health, and multi-instance topology. Read this skill before any Memcached operations.
connection_type	memcached
preload	false

Memcached Management Skill

Monitor, analyze, and optimize Memcached instances safely.

MANDATORY: Discovery-First Pattern

Always run stats commands before inspecting specific slabs or items. Never assume slab classes or item counts.

Phase 1: Discovery

#!/bin/bash

MC_HOST="${MEMCACHED_HOST:-localhost}"
MC_PORT="${MEMCACHED_PORT:-11211}"

mc_cmd() {
    echo "$1" | nc -q2 "$MC_HOST" "$MC_PORT" 2>/dev/null || \
    echo "$1" | nc -w2 "$MC_HOST" "$MC_PORT" 2>/dev/null
}

echo "=== General Stats ==="
mc_cmd "stats" | grep -E 'version|uptime|curr_connections|total_connections|curr_items|total_items|bytes |limit_maxbytes|evictions|get_hits|get_misses|cmd_get|cmd_set'

echo ""
echo "=== Hit Ratio ==="
mc_cmd "stats" | awk -F' ' '
    /get_hits/ { hits=$3 }
    /get_misses/ { misses=$3 }
    END {
        total = hits + misses
        if (total > 0) printf "Hit ratio: %.1f%% (%s hits, %s misses)\n", hits/total*100, hits, misses
        else print "No gets recorded yet"
    }'

echo ""
echo "=== Memory Usage ==="
mc_cmd "stats" | awk -F' ' '
    /^STAT bytes / { used=$3 }
    /limit_maxbytes/ { limit=$3 }
    END {
        if (limit > 0) printf "Memory: %dMB / %dMB (%.1f%%)\n", used/1048576, limit/1048576, used/limit*100
    }'

echo ""
echo "=== Slab Overview ==="
mc_cmd "stats slabs" | grep -E 'chunk_size|used_chunks|total_chunks|mem_requested' | head -20

Phase 1 outputs: Version, connection count, item count, hit ratio, memory utilization, slab allocation.

Phase 2: Analysis

#!/bin/bash

MC_HOST="${MEMCACHED_HOST:-localhost}"
MC_PORT="${MEMCACHED_PORT:-11211}"

mc_cmd() {
    echo "$1" | nc -q2 "$MC_HOST" "$MC_PORT" 2>/dev/null || \
    echo "$1" | nc -w2 "$MC_HOST" "$MC_PORT" 2>/dev/null
}

echo "=== Slab Efficiency ==="
mc_cmd "stats slabs" | awk -F'[: ]' '
    /used_chunks/ { slab=$2; used[$2]=$4 }
    /total_chunks/ { total[$2]=$4 }
    END {
        for (s in used) {
            if (total[s] > 0) printf "Slab %s: %s/%s chunks used (%.0f%%)\n", s, used[s], total[s], used[s]/total[s]*100
        }
    }' | sort -t: -k1 -n

echo ""
echo "=== Eviction Stats ==="
mc_cmd "stats items" | grep -E 'evicted|outofmemory|crawler' | head -15

echo ""
echo "=== Connection Analysis ==="
mc_cmd "stats" | grep -E 'curr_connections|listen_disabled|conn_yields|rejected_connections'

echo ""
echo "=== Growth Trends ==="
mc_cmd "stats" | grep -E 'total_items|evictions|reclaimed|expired_unfetched'

Output Format

MEMCACHED ANALYSIS
==================
Version: [version] | Uptime: [days]d
Memory: [used]/[limit] | Items: [count] | Hit Ratio: [pct]%

ISSUES FOUND:
- [issue with affected component]

RECOMMENDATIONS:
- [actionable recommendation]

Anti-Hallucination Rules

1. NEVER assume resource names — always discover via CLI/API in Phase 1 before referencing in Phase 2.
2. NEVER fabricate metric names or dimensions — verify against the service documentation or --help output.
3. NEVER mix CLI commands between service versions — confirm which version/API you are targeting.
4. ALWAYS use the discovery → verify → analyze chain — every resource referenced must have been discovered first.
5. ALWAYS handle empty results gracefully — an empty response is valid data, not an error to retry.

Counter-Rationalizations

Shortcut	Counter	Why
"I'll skip discovery and check known resources"	Always run Phase 1 discovery first	Resource names change, new resources appear — assumed names cause errors
"The user only asked for a quick check"	Follow the full discovery → analysis flow	Quick checks miss critical issues; structured analysis catches silent failures
"Default configuration is probably fine"	Audit configuration explicitly	Defaults often leave logging, security, and optimization features disabled
"Metrics aren't needed for this"	Always check relevant metrics when available	API/CLI responses show current state; metrics reveal trends and intermittent issues
"I don't have access to that"	Try the command and report the actual error	Assumed permission failures prevent useful investigation; actual errors are informative