add a counter and print out myself
On Thu, Nov 15, 2012 at 1:51 PM, Wz1975 <wz1...@yahoo.com> wrote: > Curious where did you see this? > > > Thanks. > -Wei > > Sent from my Samsung smartphone on AT&T > > > -------- Original message -------- > Subject: Re: unable to read saved rowcache from disk > From: Manu Zhang <owenzhang1...@gmail.com> > To: user@cassandra.apache.org > CC: > > > 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. >>> > >>> > >>> >>> >>> >> >
