-Iterators - updating other rows
Peter Tillotson 2013-07-15, 10:38
I've got two tables of dependent data, which I was hoping to update efficiently during compaction. This leads to the following requirements:
- Changes to other rows
- Changes in other tables
I've fought with iterators and embedding writers, but have had to fall back to map reduce jobs to complete the update.
Is there a recommended approach to this?
I bit more detail about the algorithm.
I've two tables with different sort orders, and I use ngram row ids to group element and split over multiple tablets, so:
nm: key1: 000: newValueId2
nm: key2: type: valueId1
nm: key3: type: valueId1
ab: valueId1: 001: blob
ab: valueId1:key2: nm
Multiple keys point to the same value in the other table but both keys and values are liable to changes ... what I was trying to do was use special columns (column Qaulifier 000 above), I call them care-of to do redirects as data changes real-time, with iterators this would becomes eventually consistent and be very efficiently but a MapReduce approach requires multiple table scans of each large table. I like the approach because the ngram splits / groups data and the two different sorts give me different nice query characteristics.
For some reason the embedded writers were blocking - I may retry with a larger cluster. I fought with it for a few days then resorted to MapReduce jobs until I get a chance to look at the Accumulo code more closely.
Would it be easy to add a special iterator that accepts (Text, Mutation) pairs much as the AccumuloOutputFormat does ?
Many thanks in advance