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https://issues.apache.org/jira/browse/IGNITE-640?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16526192#comment-16526192
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Anton Vinogradov commented on IGNITE-640:
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[~aakhmedov]
1) gate.enter() operates on readLock, which means it guarantee that all
operations will be finished before we'll perform some critical operation with
writeLock.
2) Better case is to use structures I listed as is.
I expect no changes at these classes, except names.
Even having that IGNITE-7823 almost ready to be merged I think that we can
rename classes as a part of this issue, this should not cause real problems at
merge.
3) Since we decided how to fix IGNITE-5553 it's a good idea to "merge" Multimap
and Set.
Both will be eventually "fixed" at IGNITE-5553.
So, as far as I understand we agreed that Multimap should be implemented based
on IgniteSet.
Common parts will be extracted to abstract classes and same datastructures will
be used.
Correct?
P.s. In case you see some more optimisation of IgniteSet (except onheap
duplication removal), let's discuss them.
> 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: 2.7
>
>
> 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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