CODEWITHSUNDEEP
statisticsmemcached
Christian Esken
Christian Esken

Reputation: 482

memcached statistics total_items is less than cmd_set

The statistics on my memcached server show a strange relationship: total_items is less than cmd_set. The only operations run on this server are "set" and "get", nothing else like "add", "replace", "delete" or CAS based operations.

When I go through the memcached source code, I see that any "normal" set (w/o CAS) will either replace or write the item, and both will increment total_items.

do_store_item() {
    // ...
    if (old_it != NULL)
        item_replace(old_it, it, hv);
    else
        do_item_link(it, hv);
    // ...
}

do_item_link() increases total_items, and item_replace() also calls do_item_link(). Then how can total_items be less than cmd_set?

Excerpt from memcached stats (numbers indented for readability):

STAT cmd_set          12827359728
STAT total_items       4237422053
STAT curr_items          60745375
STAT expired_unfetched 9898430934
STAT evicted_unfetched   30415090
STAT evictions           30421532
STAT reclaimed         9900995350

Upvotes: 0

Views: 210

Answers (1)

Christian Esken
Christian Esken

Reputation: 482

The statistics looked so strange because they are wrong. It is a memcached bug (integer overrun at 2^32). memcached developers have acknowledged and fixed it. For more details see https://github.com/memcached/memcached/issues/161.

Upvotes: 1

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