could i set some cache policy to let spark load data from tachyon only one time for all sql query? for example by using CacheAllPolicy FIFOCachePolicy LRUCachePolicy. But I have tried that three policy, they are not useful. I think , if spark always load data for each sql query, it will impact the query speed , it will take more time than the case that data are managed by spark itself.
2014-07-09 1:19 GMT+08:00 Haoyuan Li <haoyuan...@gmail.com>: > Yes. For Shark, two modes, "shark.cache=tachyon" and "shark.cache=memory", > have the same ser/de overhead. Shark loads data from outsize of the process > in Tachyon mode with the following benefits: > > > - In-memory data sharing across multiple Shark instances (i.e. stronger > isolation) > - Instant recovery of in-memory tables > - Reduce heap size => faster GC in shark > - If the table is larger than the memory size, only the hot columns will > be cached in memory > > from http://tachyon-project.org/master/Running-Shark-on-Tachyon.html and > https://github.com/amplab/shark/wiki/Running-Shark-with-Tachyon > > Haoyuan > > > On Tue, Jul 8, 2014 at 9:58 AM, Aaron Davidson <ilike...@gmail.com> wrote: > > > Shark's in-memory format is already serialized (it's compressed and > > column-based). > > > > > > On Tue, Jul 8, 2014 at 9:50 AM, Mridul Muralidharan <mri...@gmail.com> > > wrote: > > > > > You are ignoring serde costs :-) > > > > > > - Mridul > > > > > > On Tue, Jul 8, 2014 at 8:48 PM, Aaron Davidson <ilike...@gmail.com> > > wrote: > > > > Tachyon should only be marginally less performant than memory_only, > > > because > > > > we mmap the data from Tachyon's ramdisk. We do not have to, say, > > transfer > > > > the data over a pipe from Tachyon; we can directly read from the > > buffers > > > in > > > > the same way that Shark reads from its in-memory columnar format. > > > > > > > > > > > > > > > > On Tue, Jul 8, 2014 at 1:18 AM, qingyang li < > liqingyang1...@gmail.com> > > > > wrote: > > > > > > > >> hi, when i create a table, i can point the cache strategy using > > > >> shark.cache, > > > >> i think "shark.cache=memory_only" means data are managed by spark, > > and > > > >> data are in the same jvm with excutor; while > "shark.cache=tachyon" > > > >> means data are managed by tachyon which is off heap, and data are > > not > > > in > > > >> the same jvm with excutor, so spark will load data from tachyon for > > > each > > > >> query sql , so, is tachyon less efficient than memory_only cache > > > strategy > > > >> ? > > > >> if yes, can we let spark load all data once from tachyon for all > sql > > > query > > > >> if i want to use tachyon cache strategy since tachyon is more HA > than > > > >> memory_only ? > > > >> > > > > > > > > > -- > Haoyuan Li > AMPLab, EECS, UC Berkeley > http://www.cs.berkeley.edu/~haoyuan/ >
