Zabbix value cache working in low memory mode but % used always < 20%

[nunojpg]

Running 5.0.

I've got successive "Zabbix value cache working in low memory mode" triggers, and initially increased the cachesize up to 32M.

Now I got it again and I've confirmed for the past 24h my value cache % was always below 20%.




On the other hand I see this in the log:

177:20200617:080919.433 === memory statistics for value cache size ===
177:20200617:080919.433 free chunks of size 24 bytes: 4
177:20200617:080919.433 free chunks of size 32 bytes: 84
177:20200617:080919.433 free chunks of size 48 bytes: 206
177:20200617:080919.433 free chunks of size 56 bytes: 2
177:20200617:080919.433 free chunks of size 80 bytes: 2
177:20200617:080919.433 free chunks of size 144 bytes: 10
177:20200617:080919.433 free chunks of size 176 bytes: 1
177:20200617:080919.433 free chunks of size 240 bytes: 1
177:20200617:080919.436 free chunks of size >= 256 bytes: 2013
177:20200617:080919.436 min chunk size: 24 bytes
177:20200617:080919.436 max chunk size: 124976 bytes
177:20200617:080919.436 memory of total size 33554056 bytes fragmented into 16667 chunks
177:20200617:080919.436 of those, 28321912 bytes are in 2323 free chunks
177:20200617:080919.436 of those, 4965488 bytes are in 14344 used chunks
177:20200617:080919.436 ================================
177:20200617:080919.437 value cache is fully used: please increase ValueCacheSize configuration parameter


Are this unrelated?

[ingus.vilnis]

Hi,

Yes, this is a very confusing issue. Good that you posted the log fragment but there is one part of log right before, "=== most used items statistics for value cache ===".
What have you got in there?

[nunojpg]

I got a recent one:

 176:20200619:045946.640 === most used items statistics for value cache ===
176:20200619:045946.643 itemid:34855 active range:86401 hits:104934 count:3003 perc:1.432285%
176:20200619:045946.643 itemid:31353 active range:86402 hits:102952 count:2991 perc:1.426561%
176:20200619:045946.643 itemid:48027 active range:86415 hits:13385721 count:2976 perc:1.419407%
176:20200619:045946.643 itemid:32762 active range:86419 hits:13385668 count:2976 perc:1.419407%
176:20200619:045946.643 itemid:47131 active range:86416 hits:13385646 count:2976 perc:1.419407%
176:20200619:045946.643 itemid:47048 active range:86417 hits:13382771 count:2975 perc:1.418930%
176:20200619:045946.643 itemid:30936 active range:86416 hits:13339698 count:2968 perc:1.415592%
176:20200619:045946.643 itemid:35268 active range:86419 hits:13358643 count:2965 perc:1.414161%
176:20200619:045946.643 itemid:47318 active range:86417 hits:13327483 count:2965 perc:1.414161%
176:20200619:045946.643 itemid:47759 active range:86421 hits:13357176 count:2963 perc:1.413207%
176:20200619:045946.643 itemid:32764 active range:86401 hits:106560 count:2959 perc:1.411299%
176:20200619:045946.643 itemid:33362 active range:86401 hits:106560 count:2959 perc:1.411299%
176:20200619:045946.643 itemid:40986 active range:86402 hits:106560 count:2958 perc:1.410822%
176:20200619:045946.643 itemid:32515 active range:86402 hits:106536 count:2958 perc:1.410822%
176:20200619:045946.643 itemid:42514 active range:86401 hits:106560 count:2958 perc:1.410822%
176:20200619:045946.643 itemid:47050 active range:86402 hits:106560 count:2957 perc:1.410345%
176:20200619:045946.643 itemid:42379 active range:86401 hits:106512 count:2956 perc:1.409868%
176:20200619:045946.643 itemid:31517 active range:86421 hits:13331428 count:2955 perc:1.409391%
176:20200619:045946.643 itemid:31600 active range:86415 hits:13329570 count:2955 perc:1.409391%
176:20200619:045946.643 itemid:30687 active range:86417 hits:13308959 count:2954 perc:1.408914%
176:20200619:045946.643 itemid:31434 active range:86416 hits:13303183 count:2954 perc:1.408914%
176:20200619:045946.643 itemid:43566 active range:86401 hits:106433 count:2953 perc:1.408437%
176:20200619:045946.643 itemid:34687 active range:86418 hits:13290921 count:2951 perc:1.407483%
176:20200619:045946.643 itemid:33013 active range:86401 hits:106417 count:2950 perc:1.407006%
176:20200619:045946.643 itemid:32432 active range:86401 hits:106532 count:2947 perc:1.405576%
176:20200619:045946.643 ==================================================
176:20200619:045946.643 === memory statistics for value cache size ===
176:20200619:045946.644 free chunks of size 24 bytes: 1
176:20200619:045946.644 free chunks of size 32 bytes: 63
176:20200619:045946.644 free chunks of size 40 bytes: 1
176:20200619:045946.644 free chunks of size 48 bytes: 192
176:20200619:045946.644 free chunks of size 56 bytes: 1
176:20200619:045946.644 free chunks of size 80 bytes: 2
176:20200619:045946.644 free chunks of size 96 bytes: 2
176:20200619:045946.644 free chunks of size 128 bytes: 2
176:20200619:045946.644 free chunks of size >= 256 bytes: 1655
176:20200619:045946.644 min chunk size: 24 bytes
176:20200619:045946.644 max chunk size: 111168 bytes
176:20200619:045946.644 memory of total size 33554056 bytes fragmented into 14872 chunks
176:20200619:045946.644 of those, 28792176 bytes are in 1919 free chunks
176:20200619:045946.644 of those, 4523944 bytes are in 12953 used chunks
176:20200619:045946.644 ================================
176:20200619:045946.644 value cache is fully used: please increase ValueCacheSize configuration parameter

The Low memory mode started at 00:15 in the plot.

[ingus.vilnis]

I think the message appears already when you have at lease one entry where "free chunks of size" equals one.

You even don't have any items that significantly stand out in the most used items statistics.

Although the case is confusing there are two options - either increase the cache size or simply live on with the warnings.