Is it through filter.collateColumns(resolved, iters, Integer.MIN_VALUE) and then MergeIterator.get(toCollate, fcomp, reducer) but I don't know what happens hereafter? How is reconcile exactly been called?
On Mon, Oct 22, 2012 at 6:49 AM, aaron morton <aa...@thelastpickle.com>wrote: > There are two processes in cassandra that trigger Read Repair like > behaviour. > > During a DigestMismatchException is raised if the responses from the > replicas do not match. In this case another read is run that involves > reading all the data. This is the CL level agreement kicking in. > > The other "Read Repair" is the one controlled by the "read_repair_chance". > When RR is active on a request ALL up replicas are involved in the read. > When RR is not active only CL replicas are involved. When test for CL > agreement occurs synchronously to the request; the RR check > waits asynchronously to the request for all nodes in the request to return. > It then checks for consistency and repairs differences. > > From looking at the source code, I do not understand how this set is built > and I do not understand how the reconciliation is executed. > > When a DigestMismatch is detected a read is run using RepairCallback. The > callback will call the RowRepairResolver.resolve() when enough responses > have been collected. > > resolveSuperset() picks one response to the baseline, and then calls > delete() to apply row level deletes from the other responses > (ColumnFamily's). It collects the other CF's into an iterator with a filter > that returns all columns. The columns are then applied to the baseline CF > which may result in reconcile() being called. > > reconcile() is used when a AbstractColumnContainer has two versions of a > column and it wants to only have one. > > RowRepairResolve.scheduleRepairs() works out the delta for each node by > calling ColumnFamily.diff(). The delta is then sent to the appropriate node. > > > Hope that helps. > > > ----------------- > Aaron Morton > Freelance Developer > @aaronmorton > http://www.thelastpickle.com > > On 19/10/2012, at 6:33 AM, Markus Klems <markuskl...@gmail.com> wrote: > > Hi guys, > > I am looking through the Cassandra source code in the github trunk to > better understand how Cassandra's fault-tolerance mechanisms work. Most > things make sense. I am also aware of the wiki and DataStax documentation. > However, I do not understand what read repair does in detail. The method > RowRepairResolver.resolveSuperset(Iterable<ColumnFamily> versions) seems to > do the trick of merging conflicting versions of column family replicas and > builds the set of columns that need to be "repaired". From looking at the > source code, I do not understand how this set is built and I do not > understand how the reconciliation is executed. ReadRepair does not seem to > trigger a Column.reconcile() to reconcile conflicting column versions on > different servers. Does it? > > If this is not what read repair does, then: What kind of inconsistencies > are resolved by read repair? And: How are the inconsistencies resolved? > > Could someone give me a hint? > > Thanks so much, > > -Markus > > >
