Comments on: Memcached for small objects

By: Serguei

Serguei — Sat, 16 May 2009 20:26:39 +0000

Also i have 144 slabs and in first no free chunks, in others 1-2-4 is free. but there is alot of memory available. what will happen when no free chunks will left? or it is stupid question?

By: Serguei

Serguei — Sat, 16 May 2009 20:17:56 +0000

Hi, Thanks for article.

I have alot of very small objects and started to use memcached. Once it reveals many evictions but limix_maxbytes was not reached. So i concluded there is not enough memory and started to read about slabs.

I had factor 1.25 now set to 1.05 and 700Mb limit

Question 1: stats slabs

STAT 1:chunk_size 104
STAT 1:chunks_per_page 10082
STAT 1:total_pages 1
STAT 1:total_chunks 10082
STAT 1:used_chunks 10080
STAT 1:free_chunks 2
STAT 1:free_chunks_end 8964

STAT 2:chunk_size 112
STAT 2:chunks_per_page 9362
STAT 2:total_pages 1
STAT 2:total_chunks 9362
STAT 2:used_chunks 9362
STAT 2:free_chunks 0
STAT 2:free_chunks_end 6721

….. etc

chunk_size 104 – this is somewhere on compile stage? so i must recompile to decrease this value?

Question 2: each page is 1 Mb. chunks_per_page is how many chunks with size 104 i have. what total_pages means? and what is free_chunks_end?

Thanks in advance for reply,
Serguei

By: Thijs (Shenzhen)

Thijs (Shenzhen) — Mon, 20 Apr 2009 09:27:10 +0000

ah, I guess should read the man better :)

memcached -vv on startup will print it

By: Thijs (Shenzhen)

Thijs (Shenzhen) — Mon, 20 Apr 2009 09:24:54 +0000

good article! I was wondering how do you get / calculate the chunk size per slab? Just add 56 bytes and then round up the the smallest 8-byte aligned value for 32 bit systems?

By: Ever wished for more Cache per Node? - Toru Maesaka

Ever wished for more Cache per Node? - Toru Maesaka — Wed, 31 Dec 2008 11:36:28 +0000

[...] to Domas for groaning… I mean indicating this improvement opportunity and Trond for hacking [...]

By: Trond Norbye

Trond Norbye — Thu, 25 Dec 2008 13:25:38 +0000

Interesting blog article Domas! I am addressing the space efficiency as part of the work I’m doing on the storage engine work.

Btw. I’m not sure I would change the alignment inside the slabs unless you are sure that your hardware doesn’t require aligned data…