Re: [jbosscache-dev] Critical CacheMarshaller issue

Manik Surtani wrote: > > On 8 Nov 2007, at 03:00, Jason T. Greene wrote: > >> Manik Surtani wrote: >>> A nasty bug, spotted by someone in the user forum (initially as a CCE) >>> http://jira.jboss.org/jira/browse/JBCACHE-1211 >>> Copying from the JIRA: >>> "This is a nasty. What started life as an optimisation for certain >>> types of objects in a marshalled stream (Fqn, GlobalTransactio, >>> String and Serializable) has become a major limitation in that a >>> single stream can only hold up to 32767 different (not equal()) >>> instances of such objects. >>> Basically the optimisation was, for example, instead of writing >>> "hello" to a stream twice, just write it once and use a reference >>> for all subsequent times. Unfortunately this reference was encoded >>> as a short, hence the limitation of 32767. >>> Fixing this will definitely break wire compatibility with JBoss >>> Cache 2.0.0, although JBC does allow backward compatibility by >>> specifying replication version in your configuration, thanks to the >>> VersionAwareMarshaller. " >>> So I guess this mandates the need for a CacheMarshaller210. The >>> question is how do we fix this. The obvious thing is to replace the >>> short references with integers. The 2 ^ 31 - 1 number of references >>> this would allow should be plenty! The drawback though, is larger >>> streams. 4-byte refs instead of 2-byte refs can be an unnecessary >>> overhead especially if objects aren't repeated much. >> >> I wouldn't worry too much about the extra bytes. However, you could >> maintain backwards compatibility, and save the 2 bytes, by stealing >> the sign bit on the short. If byte1 & 0x80 then read 3 more bytes, >> else read only 1 more. >> > > Still wouldn't help if you needed a million Strings in a collection. > :-) Sure it would, since you get the full positive rang of a signed int (2^31 - 1). The only difference is that if its <= 32767 you write only two bytes, and when it's greater you write an encoded int that can be detected (only 4 bytes). // Writing code if (n > 32767) { n = n | 0x80000000; writeInt(n); } else { writeShort(n); } // Reading code int n = readShort(); if ((n & 0x80000000) != 0) { // sign bit rolls off n = n << 16 & readShort(); }