On Saturday, July 4, 2020 at 9:41:49 AM UTC+5:30, Dormando wrote: > > 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 memc...@googlegroups.com <javascript:>. > > 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. 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/f0c2bfe1-d65d-4b62-9a87-68fc42446c3do%40googlegroups.com.
