StefanRRichter commented on a change in pull request #6558: [FLINK-9116]
Introduce getAll and removeAll for MapState
URL: https://github.com/apache/flink/pull/6558#discussion_r210510928
##########
File path:
flink-state-backends/flink-statebackend-rocksdb/src/main/java/org/apache/flink/contrib/streaming/state/RocksDBMapState.java
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@@ -129,6 +132,36 @@ public UV get(UK userKey) throws IOException,
RocksDBException {
return (rawValueBytes == null ? null :
deserializeUserValue(rawValueBytes));
}
+ @Override
+ public Map<UK, UV> getAll(Collection<UK> keys) throws IOException,
RocksDBException {
+
+ Map<UK, byte[]> keyBytesMap = new HashMap<>(keys.size());
+ List<ColumnFamilyHandle> columnFamilyHandles = new
ArrayList<>(keys.size());
+ List<byte[]> keyBytesList = new ArrayList<>(keys.size());
+
+ for (UK key : keys) {
+ columnFamilyHandles.add(columnFamily);
+ byte[] keyByte =
serializeUserKeyWithCurrentKeyAndNamespace(key);
+ keyBytesList.add(keyByte);
+ keyBytesMap.put(key, keyByte);
+ }
+
+ Map<byte[], byte[]> result =
backend.db.multiGet(columnFamilyHandles, keyBytesList);
Review comment:
I think we should favor iterating individual keys over adding them all to a
list & multiGet. It seems more more memory efficient.
https://github.com/facebook/rocksdb/wiki/RocksDB-FAQ
> Q: If I want to retrieve 10 keys from rocksdb, is it better to batch them
and use MultiGet() versus issuing 10 individual Get() calls?
>
> A: The performance is similar. MultiGet() reads from the same consistent
view, but it is not faster.
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