EdgeHub: Fix MessageStore initial offset after restart #603
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myagley
approved these changes
Dec 5, 2018
| @@ -13,6 +14,7 @@ public static long GetOffsetFromKey(byte[] key) | |||
| Preconditions.CheckNotNull(key, nameof(key)); | |||
| if (BitConverter.IsLittleEndian) | |||
| { | |||
| key = key.ToArray(); | |||
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So, to convert the key to offset (byte array to offset, we need to reverse the byte array if the arch is little endian. But we don't want to affect the original byte array. So ToArray creates a copy of it. (I will add a comment saying so).
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EdgeHub Message store contains queues for each endpoint. 3 pointer values are maintained - head, tail, and checkpoint (where the last processed pointer was).
Of these head and tail are computed from the queue, and checkpoint is persisted.
However, in a situation where all messages are processed and cleaned up, the queue will be empty and checkpointer will be pointing to the last processed value (say 1600).
If at this point the EdgeHub is restarted, the initialized values will be -
head =0, tail = -1 and checkpoint = 1600.
This PR fixes the issue, so that the initialization values are -
head = 1600, tail = 1599, checkpoint = 1600.