[jboss-dev-forums] [Design of JBoss Transaction Services] - Re: transaction support in JBossAS 5.0

[mark.little@jboss.com]

"reverbel" wrote : "mark.little at jboss.com" wrote : However, although I understand why you're doing this reference approach, I'm not convinced it buys you much. The size of an IOR is so large anyway when compared to an Xid, that saving a few bytes is unlikely to make much of a difference on the number of blocks that get written in the log. It's the number of physical disk blocks and not the amount of information, that makes a difference.
  | The difference needs to be measured. An Xid can take up to 128 bytes, but in an IOR it will take up to 256 bytes, due to the encoding of bytes as pairs of ASCII characters that represent hex digits. This looks like a significant increase in the size of IORs, 
  | 

For small IORs, yes. However, it really depends on the ORB implementation. I've used pretty much every C++ and Java ORB that has been around since the mid 1990's and I've seen several (names withheld to protect the innocent!) where the IOR is in excess of 4K.

anonymous wrote : 
  | but it may or may not have a significant impact on the performance of marshalling, transaction context propagation, and logging tasks. The impact is more likely to be significant in the case of JBossRemoting, whose URIs are much smaller than IORs and WS-Addressing endpoint references. But it needs to be measured anyway.
  | 

Agreed. Ultimately this approach may be something that is best chosen at runtime (dynamically) by a deployer/sys admin when all of the related implications are known. Plus it may depend on what implementation of logging you're using. For example, if you use replicated NVRAM, then there's no notion of a physical block size and it may be that my previous comment doesn't apply.

anonymous wrote : 
  | It appears that we are in agreement that this is a reasonable approach, which has a conceptual advantage (it avoids nesting of globally unique identifiers), but whose practical benefits need to be validated by measurements.
  | 
  | Regards,
  | 
  | Francisco
  | 

Yes, now that I have all of the information ;-) I think it's actually quite an interested research topic. If you need any help/input, let me know.

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