For the extstore, it doesn't matter whether your data set is sharded or not as the scope is a single Memcached process. Note that data is not durable, if the Memcached process crashes, data can not be recovered.
Yes, ext_item_age=0 will write data to the disk quickly, leaving only keys + meta data in memory. It's using FS cache as it does read/readv/pread/preadv. If the probability of reading an item is high after it's written, you can increase the ext_item_age to keep it in memory. A possible downside of this is if your write rate is high, memory is full and the disk writes are slow, it will evict items before getting a chance to flush to the disk. Extstore will work with both write-once or with updates. More details are here: https://github.com/memcached/memcached/wiki/Extstore#tuning-guide. The original blog is here: https://memcached.org/blog/extstore-cloud/ On Friday, 4 December 2020 at 08:45:36 UTC-8 Jacob Eisinger wrote: > Oh, and, one more important aspect. Our data is mostly write-once, > read-many times. There are no updates today. And, in the future, there > will be very few updates. > > On Friday, December 4, 2020 at 11:05:18 AM UTC-5 Jacob Eisinger wrote: > >> >> Howdy, >> >> We are investigating using Memcached's extstore as a >> single/non-sharded/non-clustered application cache of data larger than >> memory. From my reading, it sounds like this is not the typical use case. >> Due to that, I wanted to see if there were any unintended consequences of >> our configuration. >> >> Specifically, we are looking to configure extstore with ext_item_age=0. >> From our initial testing, it looks like this means that this effectively >> turns Memcached into a mostly disk-based cache of values. In particular, >> Memcached will attempt to write out pages as soon as they fill to disk. >> Then, when accessing values, the disk cache -> disk will be used. Is that >> correct? >> >> We noticed the extstore file grows and the memcache memory stays >> relatively low. If we wanted to keep more of the recent values in memory, >> should we just increase the ext_item_age to a couple of hours? Are there >> unintended consequences of this setup? Any other configuration that we >> should be looking at? >> >> Cheers, >> Jacob >> > -- --- 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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/memcached/6389b256-1204-47bc-b52e-5df3d63ef0a3n%40googlegroups.com.
