6720a01733
Kinesis allows clients to rely on an invariant that, for a given partition key, the order of records added to the stream will be maintained. IE: given an input `pkey=x,val=1 pkey=x,val=2 pkey=x,val=3`, the values `1,2,3` will be seen in that order when processed by clients, so long as clients are careful. It does so by putting all records for a single partition key into a single shard, then maintaining ordering within that shard.
However, shards can be split and merge, to distribute load better and handle per-shard throughput limits. Kinesis does this currently by (one or many times) splitting a single shard into two or by merging two adjacent shards into one. When this occurs, Kinesis still allows for ordering consistency by detailing shard parent/child relationships within its `listShards` outputs. A split shard A will create children B and C, both with `ParentShardId=A`. A merging of shards A and B into C will create a new shard C with `ParentShardId=A,AdjacentParentShardId=B`. So long as clients fully process all records in parents (including adjacent parents) before processing the new shard, ordering will be maintained.
`kinesis-consumer` currently doesn't do this. Instead, upon the initial (and subsequent) `listShards` call, all visible shards immediately begin processing. Considering this case, where shards split, then merge, and each shard `X` contains a single record `rX`:
```
time ->
B
/ \
A D
\ /
C
```
record `rD` should be processed after both `rB` and `rC` are processed, and both `rB` and `rC` should wait for `rA` to be processed. By starting goroutines immediately, any ordering of `{rA,rB,rC,rD}` might occur within the original code.
This PR utilizes the `AllGroup` as a book-keeper of fully processed shards, with the `Consumer` calling `CloseShard` once it has finished a shard. `AllGroup` doesn't release a shard for processing until its parents have fully been processed, and the consumer just processes the shards it receives as it used to.
This PR created a new `CloseableGroup` interface rather than append to the existing `Group` interface to maintain backwards compatibility in existing code that may already implement the `Group` interface elsewhere. Different `Group` implementations don't get the ordering described above, but the default `Consumer` does.
21 lines
584 B
Go
21 lines
584 B
Go
package consumer
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import (
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"context"
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"github.com/aws/aws-sdk-go-v2/service/kinesis/types"
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)
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// Group interface used to manage which shard to process
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type Group interface {
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Start(ctx context.Context, shardc chan types.Shard)
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GetCheckpoint(streamName, shardID string) (string, error)
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SetCheckpoint(streamName, shardID, sequenceNumber string) error
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}
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type CloseableGroup interface {
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Group
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// Allows shard processors to tell the group when the shard has been
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// fully processed. Should be called only once per shardID.
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CloseShard(ctx context.Context, shardID string) error
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}
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