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https://issues.apache.org/jira/browse/IGNITE-640?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16501233#comment-16501233
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Amir Akhmedov commented on IGNITE-640:
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Hi [~avinogradov],
Thanks for your time to review and comment my changes. Please find below my
comments:
# I think Map and Set look similar at first glance but in general they
implement two different interfaces which has nothing in common. In terms of
Ignite we can build similar infrastructure on CacheDataStructuresManager and
DataStructuresProcessor levels but I doubt we can come up with generic easy
maintainable design for both of them.
# Agree. I could say the methods queue0 and multimap0 in
CacheDataStructuresManager are identical and would be nice to merge them into
one but I can't make my mind how to do this cause despite having the similar
flow those methods operate with different object types, arguments, predicates
etc. If you have an idea how to converge them would be happy to listen to it.
# Fixed.
# Fixed in most places. Will look more carefully in next days.
# Fixed.
# Sorry, I'm not following. Can you please put more details how
GridCacheMultimapApiSelfAbstractTest could be shortened?
# Fixed.
# Fixed.
# I tried my best and did something wrong, now my PR looks ugly :) I don't
know can it be reverted back or not.
Please let me know if you have any other inquiries or concerns.
> Implement IgniteMultimap data structures
> ----------------------------------------
>
> Key: IGNITE-640
> URL: https://issues.apache.org/jira/browse/IGNITE-640
> Project: Ignite
> Issue Type: Sub-task
> Components: data structures
> Reporter: Dmitriy Setrakyan
> Assignee: Amir Akhmedov
> Priority: Major
> Fix For: 2.6
>
>
> We need to add {{IgniteMultimap}} data structure in addition to other data
> structures provided by Ignite. {{IgniteMultiMap}} should have similar API to
> {{java.util.Map}} class in JDK, but support the semantics of multiple values
> per key, similar to [Guava
> Multimap|http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/collect/Multimap.html].
>
> However, unlike in Guava, our multi-map should work with Lists, not
> Collections. Lists should make it possible to support the following methods:
> {code}
> // Gets value at a certain index for a key.
> V get(K, index);
> // Gets all values for a collection of keys at a certain index.
> Map<K, V> getAll(Collection<K>, index);
> // Gets values for specified indexes for a key.
> List<V> get(K, Iterable<Integer> indexes);
> // Gets all values for a collection of keys at specified indexes.
> Map<K, Collection<V>> getAll(Collection<K>, Iterable<Integer> indexes);
> // Gets values for specified range of indexes, between min and max.
> List<V> get(K, int min, int max);
> // Gets all values for a collection of keys for a specified index range,
> between min and max.
> Map<K, Collection<V>> getAll(Collection<K>, int min, int max);
> // Gets all values for a specific key.
> List<V> get(K);
> // Gets all values for a collection of keys.
> Map<K, List<V>> getAll(Collection<K>);
> // Iterate through all elements with a certain index.
> Iterator<Map.Entry<K, V>> iterate(int idx);
> // Do we need this?
> Collection<IgniteTuple<Integer V>> get(K, IgniteBiPredicate<Integer, V>)
> {code}
> Multimap should also support colocated and non-colocated modes, similar to
> [IgniteQueue|https://github.com/apache/incubator-ignite/blob/master/modules/core/src/main/java/org/apache/ignite/IgniteQueue.java]
> and its implementation,
> [GridAtomicCacheQueueImpl|https://github.com/apache/incubator-ignite/blob/master/modules/core/src/main/java/org/apache/ignite/internal/processors/datastructures/GridAtomicCacheQueueImpl.java].
> h2. Design Details
> The most natural way to implement such map, would be to store every value
> under a separate key in an Ignite cache. For example, let's say that we have
> a key {{K}} with multiple values: {{V0, V1, V2, ...}}. Then the cache should
> end up with the following values {{K0, V0}}, {{K1, V1}}, {{K2, V2}}, etc.
> This means that we need to wrap user key into our own, internal key, which
> will also have {{index}} field.
> Also note that we need to collocate all the values for the same key on the
> same node, which means that we need to define user key K as the affinity key,
> like so:
> {code}
> class MultiKey<K> {
> @CacheAffinityMapped
> private K key;
> int index;
> }
> {code}
> Look ups of values at specific indexes becomes very simple. Just attach a
> specific index to a key and do a cache lookup. Look ups for all values for a
> key should work as following:
> {code}
> MultiKey key;
> V v = null;
> int index = 0;
> List<V> res = new LinkedList<>();
> do {
> v = cache.get(MultiKey(K, index));
> if (v != null)
> res.add(v);
> index++;
> }
> while (v != null);
> return res;
> {code}
> We could also use batching for performance reason. In this case the batch
> size should be configurable.
> {code}
> int index = 0;
> List<V> res = new LinkedList<>();
> while (true) {
> List<Key> batch = new ArrayList<>(batchSize);
> // Populate batch.
> for (; index < batchSize; index++)
> batch.add(new MultiKey(K, index % batchSize);
> Map<Key, V> batchRes = cache.getAll(batch);
> // Potentially need to properly sort values, based on the key order,
> // if the returning map does not do it automatically.
> res.addAll(batchRes.values());
> if (res.size() < batch.size())
> break;
> }
> return res;
> {code}
> h2. Evictions
> Evictions in the {{IgniteMultiMap}} should have 2 levels: maximum number of
> keys, and maximum number of values for a key. The maximum number of keys
> should be controlled by Ignite standard eviction policy. The maximum number
> of values for a key should be controlled by the implementation of the
> multi-map. Either eviction parameter should be configurable.
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