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From Raymond Wilson <raymond_wil...@trimble.com>
Subject RE: Efficiently determining if cache keys belong to the local server node
Date Mon, 16 Apr 2018 20:35:58 GMT
Hi Stan,

Your understanding is correct.

I'm aware of the AffinityRun and AffinityCall methods, and their simple key

My use case may require 100,000 or more elements of information to be
processed, so I don't want to call AffinityRun/Call that often. Each of
these elements is identified by a key that is very efficiently encoded into
the request (at the ~1 bit per key  level)

Further, each of those elements identifies work units that in themselves
could have 100,000 or more different elements to be processed.

One approach would be to explicitly break up the request into smaller ones,
each targeted at a server node. But that requires the requestor to have
intimate knowledge of the composition of the grid resources deployed, which
is not desirable.

The approach I'm looking into here is to have each server node receive the
same request via Cluster.Broadcast(), and for those nodes to determine which
elements in the overall request via the Key -> Partition affinity mapping.
The mapping itself is very efficient, and as I noted in my original post
determining the partition -> node map seems simple enough to do.

I'm unsure of the performance of requesting that mapping for every request,
versus caching it and adding watchers for rebalancing and topology change
events to invalidate that cache mapping as needed (and how to wire those


-----Original Message-----
From: Stanislav Lukyanov [mailto:stanlukyanov@gmail.com]
Sent: Tuesday, April 17, 2018 12:02 AM
To: user@ignite.apache.org
Subject: RE: Efficiently determining if cache keys belong to the local
server node

// Bcc’ing off dev@ignite list for now as it seems to be rather a user-space


Let me take a step back first. It seems a bit like an XY problem
so I’d like to clarify the goals before diving into your current solution.

AFAIU you want to process certain entries in your cache locally on the
server that caches these entries. Is that correct?
Have you looked at affinityRun and affinityCall
(https://apacheignite.readme.io/docs/collocate-compute-and-data)? If yes,
why they don’t work for you?
One limitation with these methods is that they accept a single key to
process. Can you process your keys one by one, or do you need to access
multiple keys at once?


From: Raymond Wilson
Sent: 15 апреля 2018 г. 10:55
To: user@ignite.apache.org
Cc: dev@ignite.apache.org
Subject: Efficiently determining if cache keys belong to the local server

I have a type of query that asks for potentially large numbers of
information elements to be computed. Each element has an affinity key that
maps it to a server node through an IAffinityFunction.

The way the question is asked means that a single query broadcast to the
compute projection (owning the cache containing the source data for the
request) contains the identities of all the pieces of information needed to
be processed.

Each server node then scans the elements requested and identifies which ones
are its responsibility according to the affinity key.

Calculating the partition ID from the affinity key is simple (I have an
affinity function set up and supplied to the cache configuration, or I could
use IAffinity.GetPartition()), so the question became: How do I know the
server node executing the query is responsible for that partition, and so
should process this element? IE: I need to derive the vector of primary or
backup  partitions that this node is responsible for.

I can query the partition map and return it, like this:

        ICacheAffinity affinity = Cache.Ignite.GetAffinity(Cache.Name);

        public Dictionary<int, bool> primaryPartitions =
=> k, v => true);

This lets me do a dictionary lookup, but its less efficient that having a
complete partition map with simple array lookup semantics, like this:

            ICacheAffinity affinity = Cache.Ignite.GetAffinity(Cache.Name);

            bool[] partitionMap = new bool[affinity.Partitions];

            foreach (int partition in

                partitionMap[partition] = true;

This is a nice lookup for the query to determine which elements are its
responsibility from the overall request.

I’m not sure of the performance profile of this approach if I end up doing
it a lot, so I’m considering caching this lookup and invalidate it if any
event occurs that could modify the key -> partition map.


   1. How big is the penalty when determining the full partition map like
   2. If I decide to invalidate the cached map, what are all the events I’d
   need to listen to?
      1. Rebalancing events?:I found CacheRebalancingEvent, but I’m not
      sure if this gives visibility to the points in time when a rebalanced
      partition becomes active on the new node and so the partition map
      2. Topology change events? (eg: adding a new backup node without
      rebalancing (if that is a thing) I looked for an event like that but
      not found it so far, though I do know the affinity function can
respond to
      this via AssignPartitions()
   3. How do I provide my own affinity key mapper to for keys to partition
   IDs, but allow Ignite to map the partitions to nodes. The
   implementation requires both steps to be implemented. I’d prefer not to
   have the partition -> server mapping responsibility as this requires
   persistent configuration on the nodes to ensure stable mapping.



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