Memcached 1.6.34+ extstore Hybrid RAM + NVMe Flash Config

Supanote Core Team @supanote · 2 min read

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Verified Blueprint Memcached 1.6.34+

Scale Memcached capacity 5-10x at fraction of DRAM cost using 1.6.34+ extstore NVMe flash tiering, segmented LRU, and slab_automove.

✓ Keeps compact hash table & item headers in DRAM while streaming values >= 1KB onto fast NVMe storage
✓ Benefits from Memcached 1.6.34+ deterministic LRU-tail page eviction and extstore_memory_pressure metrics
✓ Disables UDP (-U 0) and enables dynamic slab page reassignment against slab calcification

Quick Fetch

# Memcached 1.6.34+ Hybrid DRAM + NVMe Flash (extstore) Systemd Environment
# Place in /etc/sysconfig/memcached or /etc/default/memcached
# Architecture: 16 GB RAM (keys, headers & hot small items) + 128 GB dedicated NVMe file

PORT="11211"
USER="memcached"
MAXCONN="8192"
# 16384 MB DRAM ceiling for hash table, metadata headers, and items < ext_item_size
CACHESIZE="16384"

# Security & Networking: Disable UDP (-U 0), bind internal interface, 8 worker threads
# Extended (-o) options:
#   modern               = Segmented HOT/WARM/COLD LRU +slab_reassign +lru_crawler +lru_maintainer
#   slab_automove=1      = Automatically move 1MB pages across slab classes as item sizes shift
#   ext_path             = Dedicated NVMe file path & capacity (pre-create directory on local XFS/ext4 NVMe)
#   ext_item_size=1024   = Offload values >= 1 KB to NVMe; keep tiny counters/flags purely in DRAM
#   ext_wbuf_size=8      = 8 MB sequential write buffer (minimizes SSD write amplification)
#   ext_threads=6        = Dedicated async disk reader/writer threads
#   ext_compact_under=4  = Compact sparse flash pages when free fragments exceed threshold
OPTIONS="-l 127.0.0.1 -U 0 -t 8 -o modern,slab_automove=1,ext_path=/var/lib/memcached-nvme/extstore.bin:128G,ext_item_size=1024,ext_wbuf_size=8,ext_threads=6"

# --- Live Health & Headroom Telemetry (run via socat / nc) ---
# printf "stats extstore
quit
" | nc -U /run/memcached/memcached.sock || nc 127.0.0.1 11211
# Watch:
#   extstore_memory_pressure (target < 80%; 100% means RAM header headroom is full)
#   extstore_bytes_used / extstore_page_evictions / extstore_io_queue

1# Memcached 1.6.34+ Hybrid DRAM + NVMe Flash (extstore) Systemd Environment

2# Place in /etc/sysconfig/memcached or /etc/default/memcached

3# Architecture: 16 GB RAM (keys, headers & hot small items) + 128 GB dedicated NVMe file

5PORT="11211"

6USER="memcached"

7MAXCONN="8192"

8# 16384 MB DRAM ceiling for hash table, metadata headers, and items < ext_item_size

9CACHESIZE="16384"

11# Security & Networking: Disable UDP (-U 0), bind internal interface, 8 worker threads

12# Extended (-o) options:

13# modern = Segmented HOT/WARM/COLD LRU +slab_reassign +lru_crawler +lru_maintainer

14# slab_automove=1 = Automatically move 1MB pages across slab classes as item sizes shift

15# ext_path = Dedicated NVMe file path & capacity (pre-create directory on local XFS/ext4 NVMe)

16# ext_item_size=1024 = Offload values >= 1 KB to NVMe; keep tiny counters/flags purely in DRAM

17# ext_wbuf_size=8 = 8 MB sequential write buffer (minimizes SSD write amplification)

18# ext_threads=6 = Dedicated async disk reader/writer threads

19# ext_compact_under=4 = Compact sparse flash pages when free fragments exceed threshold

20OPTIONS="-l 127.0.0.1 -U 0 -t 8 -o modern,slab_automove=1,ext_path=/var/lib/memcached-nvme/extstore.bin:128G,ext_item_size=1024,ext_wbuf_size=8,ext_threads=6"

22# --- Live Health & Headroom Telemetry (run via socat / nc) ---

23# printf "stats extstore

24quit

25" | nc -U /run/memcached/memcached.sock || nc 127.0.0.1 11211

26# Watch:

27# extstore_memory_pressure (target < 80%; 100% means RAM header headroom is full)

28# extstore_bytes_used / extstore_page_evictions / extstore_io_queue

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