So I was just reading and thinking about this, and I don't understand the advice offered under "Read-before-Write" at http://wiki.basho.com/Client-Implementation-Guide.html.
"Riak will return an encoded vector clock<http://wiki.basho.com/Vector-Clocks.html> > with every "fetch" or "read" request that does not result in a "not > found" response. In addition to the Client ID, this vector clock tells Riak > how to resolve concurrent writes, essentially representing the "last seen" > version of the object to which the client made modifications. In order to > prevent sibling > explosion<http://wiki.basho.com/Vector-Clocks.html#Sibling-explosion>, > clients should always have a vector clock before sending a write, and send > the vector clock as part of the write request. Therefore, it is essential > that keys are fetched before being written (except in the case where Riak > selects the key or there is *a priori* knowledge that the key is new). > Client libraries that make this automatic will reduce operational issues by > limiting sibling explosion. Clients may also choose to perform automatic > Sibling > Resolution<http://wiki.basho.com/Client-Implementation-Guide.html#Sibling-Resolution> > on read." I'm having trouble understanding the advice. I get that if I'm aware of all the siblings, I can resolve them (optionally) with that vector clock. What I don't understand here: If an application PUTs to an object out of the blue, not having read it first, should the client library read-before-write? This seems like a great way to blow away siblings by accident. I'm having trouble understanding the advice. I get that if I'm aware of all the siblings, I can resolve them (optionally) with that vector clock. What I don't understand here: If an application PUTs to an object out of the blue, not having read it first, should the client library read-before-write? This seems like a great way to blow away siblings by accident. Or is the point rather to avoid sibling explosion for applications that don't care about losing information? -- Andres
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