OOM at deserializing 747321th row
On Thu, Nov 15, 2012 at 9:08 AM, Manu Zhang <owenzhang1...@gmail.com> wrote: > oh, as for the number of rows, it's 1650000. How long would you expect it > to be read back? > > > On Thu, Nov 15, 2012 at 3:57 AM, Wei Zhu <wz1...@yahoo.com> wrote: > >> Good information Edward. >> For my case, we have good size of RAM (76G) and the heap is 8G. So I set >> the row cache to be 800M as recommended. Our column is kind of big, so the >> hit ratio for row cache is around 20%, so according to datastax, might just >> turn the row cache altogether. >> Anyway, for restart, it took about 2 minutes to load the row cache >> >> INFO [main] 2012-11-14 11:43:29,810 AutoSavingCache.java (line 108) >> reading saved cache /var/lib/cassandra/saved_caches/XXX-f2-RowCache >> INFO [main] 2012-11-14 11:45:12,612 ColumnFamilyStore.java (line 451) >> completed loading (102801 ms; 21125 keys) row cache for XXX.f2 >> >> Just for comparison, our key is long, the disk usage for row cache is >> 253K. (it only stores key when row cache is saved to disk, so 253KB/ 8bytes >> = 31625 number of keys). It's about right... >> So for 15MB, there could be a lot of "narrow" rows. (if the key is Long, >> could be more than 1M rows) >> >> Thanks. >> -Wei >> ------------------------------ >> *From:* Edward Capriolo <edlinuxg...@gmail.com> >> *To:* user@cassandra.apache.org >> *Sent:* Tuesday, November 13, 2012 11:13 PM >> *Subject:* Re: unable to read saved rowcache from disk >> >> http://wiki.apache.org/cassandra/LargeDataSetConsiderations >> >> A negative side-effect of a large row-cache is start-up time. The >> periodic saving of the row cache information only saves the keys that >> are cached; the data has to be pre-fetched on start-up. On a large >> data set, this is probably going to be seek-bound and the time it >> takes to warm up the row cache will be linear with respect to the row >> cache size (assuming sufficiently large amounts of data that the seek >> bound I/O is not subject to optimization by disks) >> >> Assuming a row cache 15MB and the average row is 300 bytes, that could >> be 50,000 entries. 4 hours seems like a long time to read back 50K >> entries. Unless the source table was very large and you can only do a >> small number / reads/sec. >> >> On Tue, Nov 13, 2012 at 9:47 PM, Manu Zhang <owenzhang1...@gmail.com> >> wrote: >> > "incorrect"... what do you mean? I think it's only 15MB, which is not >> big. >> > >> > >> > On Wed, Nov 14, 2012 at 10:38 AM, Edward Capriolo < >> edlinuxg...@gmail.com> >> > wrote: >> >> >> >> Yes the row cache "could be" incorrect so on startup cassandra verify >> they >> >> saved row cache by re reading. It takes a long time so do not save a >> big row >> >> cache. >> >> >> >> >> >> On Tuesday, November 13, 2012, Manu Zhang <owenzhang1...@gmail.com> >> wrote: >> >> > I have a rowcache provieded by SerializingCacheProvider. >> >> > The data that has been read into it is about 500MB, as claimed by >> >> > jconsole. After saving cache, it is around 15MB on disk. Hence, I >> suppose >> >> > the size from jconsole is before serializing. >> >> > Now while restarting Cassandra, it's unable to read saved rowcache >> back. >> >> > By "unable", I mean around 4 hours and I have to abort it and remove >> cache >> >> > so as not to suspend other tasks. >> >> > Since the data aren't huge, why Cassandra can't read it back? >> >> > My Cassandra is 1.2.0-beta2. >> > >> > >> >> >> >
