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From "Steinmaurer, Thomas" <thomas.steinmau...@dynatrace.com>
Subject RE: Row Cache hit issue
Date Wed, 20 Sep 2017 05:38:02 GMT
Hi,

additionally, with saved (key) caches, we had some sort of corruption (I think, for whatever
reason) once. So, if you see something like that upon Cassandra startup:

INFO [main] 2017-01-04 15:38:58,772 AutoSavingCache.java (line 114) reading saved cache /var/opt/xxx/cassandra/saved_caches/ks-cf-KeyCache-b.db
ERROR [main] 2017-01-04 15:38:58,891 CassandraDaemon.java (line 571) Exception encountered
during startup
java.lang.OutOfMemoryError: Java heap space
                at java.util.ArrayList.<init>(ArrayList.java:152)
                at org.apache.cassandra.db.RowIndexEntry$Serializer.deserialize(RowIndexEntry.java:132)
                at org.apache.cassandra.service.CacheService$KeyCacheSerializer.deserialize(CacheService.java:365)
                at org.apache.cassandra.cache.AutoSavingCache.loadSaved(AutoSavingCache.java:119)
                at org.apache.cassandra.db.ColumnFamilyStore.<init>(ColumnFamilyStore.java:276)
                at org.apache.cassandra.db.ColumnFamilyStore.createColumnFamilyStore(ColumnFamilyStore.java:435)
                at org.apache.cassandra.db.ColumnFamilyStore.createColumnFamilyStore(ColumnFamilyStore.java:406)
                at org.apache.cassandra.db.Keyspace.initCf(Keyspace.java:322)
                at org.apache.cassandra.db.Keyspace.<init>(Keyspace.java:268)
                at org.apache.cassandra.db.Keyspace.open(Keyspace.java:110)
                at org.apache.cassandra.db.Keyspace.open(Keyspace.java:88)
                at org.apache.cassandra.service.CassandraDaemon.setup(CassandraDaemon.java:364)
                at org.apache.cassandra.service.CassandraDaemon.activate(CassandraDaemon.java:554)
                at org.apache.cassandra.service.CassandraDaemon.main(CassandraDaemon.java:643)

resulting in Cassandra going OOM, with a “reading saved cache” log entry close before
the OOM, you may have hit some sort of corruption. Workaround is to physically delete the
saved cache file and Cassandra will start up just fine.

Regards,
Thomas


From: Dikang Gu [mailto:dikang85@gmail.com]
Sent: Mittwoch, 20. September 2017 06:06
To: cassandra <user@cassandra.apache.org>
Subject: Re: Row Cache hit issue

Hi Peng,

C* periodically saves cache to disk, to solve cold start problem. If row_cache_save_period=0,
it means C* does not save cache to disk. But the cache is still working, if it's enabled in
table schema, just the cache will be empty after restart.

--Dikang.

On Tue, Sep 19, 2017 at 8:27 PM, Peng Xiao <2535053@qq.com<mailto:2535053@qq.com>>
wrote:
And we are using C* 2.1.18.


------------------ Original ------------------
From:  "我自己的邮箱";<2535053@qq.com<mailto:2535053@qq.com>>;
Date:  Wed, Sep 20, 2017 11:27 AM
To:  "user"<user@cassandra.apache.org<mailto:user@cassandra.apache.org>>;
Subject:  Row Cache hit issue

Dear All,

The default row_cache_save_period=0,looks Row Cache does not work in this situation?
but we can still see the row cache hit.

Row Cache              : entries 202787, size 100 MB, capacity 100 MB, 3095293 hits, 6796801
requests, 0.455 recent hit rate, 0 save period in seconds

Could anyone please explain this?

Thanks,
Peng Xiao



--
Dikang

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