I'm a bit confused as to what you mean "if an iterator goes down
mid-processing." If it goes down at all, then whatever scope it's running
in- minor compaction, major compaction and scan- will most likely go down
as well (unless your iterator eats an exception and ignores errors). A
WALog shouldn't be deleted if whatever you were trying to do failed.
On Sat, Sep 15, 2012 at 1:44 AM, Sukant Hajra <[EMAIL PROTECTED]>wrote:
> Hi guys,
> We've been slowing inching towards using iterators more effectively. The
> typical use case of indexed docs fit one of our needs and we wrote a
> for it.
> We've recently realized that iterators are not just read-only, and that we
> get more data-local functionality by taking advantage of their ability to
> mutate data as well. We've only begun to think more of how this may
> assist us.
> A /lot/ of our critical data-accesses are slightly complex, but local to
> row. We have billions of entities in our system, so a simple bijection of
> entities to rows works our really well for us with respect to iterators.
> Up to this point, we've had an planned architecture that uses Kestrel for
> and a messaging system like Akka pipelining work. Akka would help us
> flowing work from the user to the log and from the log to orchestrations of
> Accumulo intra-row reads and writes. The log just helps us get some faster
> response time without sacrificing too much reliability.
> Recently someone asked why use our own WALog when Accumulo has one
> natively in
> HDFS. My response has been that Accumulo's WALog is at a lower level of
> granularity of mutations. We want reliable orchestrations of mutations.
> orchestrations are idempotent, but we want something long the lines of
> at-least-once delivery for the entire orchestration. If an iterator goes
> mid-processing, I fear Accumulo's native WALog is insufficient to claim we
> a reliable enough system.
> I could definitely go through source code to validate this opinion, but I
> thought I'd bounce this reasoning off the list first.
> Also, I'm sure we're not the only people using Accumulo in this way.
> feel to advise us if anyone's got other ideas for an architecture or feels
> we're thinking about the problem backwards.
> Thanks for your input,