No attachment On Fri, 3 Jul 2020, Shweta Agrawal wrote:
> > Wooo...so quick. :):) > > Correct, close. It actually uses more like 3 512k chunks and then one > > smaller chunk from a different class to fit exactly 1.6MB. > I see.Got it. > > >Can you share snapshots from "stats items" and "stats slabs" for one of > these instances? > > Currently I have summary of it, sharing the same below. I can get snapshot by > Tuesday as need to request for it. > > pages have value from total_pages from stats slab for each slab > item_size have value from chunk_size from stats slab for each slab > Used memory is calculated as pages*page size ---> This has to corrected now. > > > prod_stats.png > > > > 90%+ are perfectly doable. You probably need to look a bit more closely > > into why you're not getting the efficiency you expect. The detailed stats > > output should point to why. I can help with that if it's confusing. > > Great. Will surely ask for your input whenever I have question. It is really > kind of you to offer help. > > > Either the slab rebalancer isn't keeping up or you actually do have 39GB > > of data and your expecations are a bit off. This will also depending on > > the TTL's you're setting and how often/quickly your items change size. > > Also things like your serialization method / compression / key length vs > > data length / etc. > > We have much less data than 39 GB. As after facing evictions, it has been > always kept higher than expected data-size. > TTL is two days or more. > From my observation items size(data-length) is in the range of 300Bytes to > 500K after compression. > Key length is in the range of 40-80 bytes. > > Thank you, > Shweta > > On Saturday, July 4, 2020 at 8:38:31 AM UTC+5:30, Dormando wrote: > Hey, > > > Putting my understanding to re-confirm: > > 1) Page size will always be 1MB and we cannot change it.Moreover, > it's not required to be changed. > > Correct. > > > 2) We can store items larger than 1MB and it is done by combining > chunks together. (example: let's say item size: ~1.6MB --> 4 slab > chunks(512k slab) from > > 2 pages will be used) > > Correct, close. It actually uses more like 3 512k chunks and then one > smaller chunk from a different class to fit exactly 1.6MB. > > > We use memcache in production and in past we saw evictions even when > free memory was present. Also currently we use cluster with 39GB RAM in > total to > > cache data even when data size we expect is ~15GB to avoid eviction > of active items. > > Can you share snapshots from "stats items" and "stats slabs" for one of > these instances? > > > But as our data varies in size, it is possible to avoid evictions by > tuning parameters: chunk_size, growth_factor, slab_automove. Also I > believe memcache > > is efficient and we can reduce cost by reducing memory size for > cluster. > > So I am trying to find the best possible memory size and parameters > we can have.So want to be clear with my understanding and calculations. > > > > So while trying different parameters and putting all calculations, I > observed that total_pages * item_size_max > physical memory for a > machine. And from > > all blogs,and docs it didnot match my understanding. But it's clear > now. Thanks to you. > > > > One last question: From my trials I find that we can achieve ~90% > storage efficiency with memcache. (i.e we need 10MB of physical memory to > store 9MB of > > data. Do you recommend any idle memory-size interms of percentage of > expected data-size? > > 90%+ are perfectly doable. You probably need to look a bit more closely > into why you're not getting the efficiency you expect. The detailed > stats > output should point to why. I can help with that if it's confusing. > > Either the slab rebalancer isn't keeping up or you actually do have 39GB > of data and your expecations are a bit off. This will also depending on > the TTL's you're setting and how often/quickly your items change size. > Also things like your serialization method / compression / key length vs > data length / etc. > > -Dormando > > > On Saturday, July 4, 2020 at 12:23:09 AM UTC+5:30, Dormando wrote: > > Hey, > > > > Looks like I never updated the manpage. In the past the item > size max was > > achieved by changing the slab page size, but that hasn't been > true for a > > long time. > > > > From ./memcached -h: > > -m, --memory-limit=<num> item memory in megabytes (default: 64) > > > > ... -m just means the memory limit in megabytes, abstract from > the page > > size. I think that was always true. > > > > In any recentish version, any item larger than half a page size > (512k) is > > created by stitching page chunks together. This prevents waste > when an > > item would be more than half a page size. > > > > Is there a problem you're trying to track down? > > > > I'll update the manpage. > > > > On Fri, 3 Jul 2020, Shweta Agrawal wrote: > > > > > Hi, > > > Sorry if I am repeating the question, I searched the list but > could not find definite answer. So posting it. > > > > > > Memcache version: 1.5.10 > > > I have started memcahce with option: -I 4m (setting maximum > item size to 4MB).Verified it is set by command stats settings , I can > see STAT > > item_size_max > > > 4194304. > > > > > > Documentation from git repository here stats that: > > > > > > -I, --max-item-size=<size> > > > Override the default size of each slab page. The default size > is 1mb. Default > > > value for this parameter is 1m, minimum is 1k, max is 1G > (1024 * 1024 * 1024). > > > Adjusting this value changes the item size limit. > > > My understanding from documentation is this option will allow > to save items with size till 4MB and the page size for each slab will > be 4MB > > (as I set it as > > > -I 4m). > > > > > > I am able to save items till 4MB but the page-size is still > 1MB. > > > > > > -m memory size is default 64MB. > > > > > > Calculation: > > > -> Calculated total pages used from stats slabs output > parameter total_pages = 64 (If page size is 4MB then total pages should not > be more > > than 16. Also > > > when I store 8 items of ~3MB it uses 25 pages but if page > size is 4MB, it should use 8 pages right.) > > > > > > Can you please help me in understanding the behaviour? > > > > > > Attached files with details for output of command stats > settings and stats slabs. > > > Below is the summarized view of the distribution. > > > First added items with variable sizes, then then added items > with 3MB and above. > > > > > > data_distribution.png > > > > > > > > > > > > Please let me know in case more details are required or > question is not clear. > > > > > > Thank You, > > > Shweta > > > > > > -- > > > > > > --- > > > You received this message because you are subscribed to the > Google Groups "memcached" group. > > > To unsubscribe from this group and stop receiving emails from > it, send an email to memc...@googlegroups.com. > > > To view this discussion on the web visit > > > https://groups.google.com/d/msgid/memcached/2b640e1f-9f59-4432-a930-d830cbe8566do%40googlegroups.com. > > > > > > > > > > -- > > > > --- > > You received this message because you are subscribed to the Google > Groups "memcached" group. > > To unsubscribe from this group and stop receiving emails from it, > send an email to memc...@googlegroups.com. > > To view this discussion on the web visit > > https://groups.google.com/d/msgid/memcached/586aad58-c6fb-4ed8-89ce-6b005d59ba12o%40googlegroups.com. > > > > > > prod_stats.png > > -- > > --- > You received this message because you are subscribed to the Google Groups > "memcached" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to memcached+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/memcached/8d011c1a-deec-463f-a17e-4e9908d97bdfo%40googlegroups.com. > > -- --- You received this message because you are subscribed to the Google Groups "memcached" group. 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