Optimise memberlist kv store access by storing data unencoded. #4345
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stevesg
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tomwilkie
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The following profile data was taken from running 50 idle ingesters with
memberlist, with almost everything at default values (5s heartbeats):
```
52.16% mergeBytesValueForKey
+- 52.16% mergeValueForKey
+- 47.84% computeNewValue
+- 27.24% codec Proto Decode
+- 26.25% mergeWithTime
```
It is apparent from the this that a lot of time is spent on the memberlist
receive path, as might be expected, specifically, the merging of the update
into the current state. The cost however is not in decoding the incoming
states (occurs in `mergeBytesValueForKey` before `mergeValueForKey`), but
in fact decoding _current state_ of the value in the store (as it is stored
encoded). The ring state was measured at 123K (50 ingesters), so it makes
sense that decoding could be costly.
This can be avoided by storing the value in it's decoded `Mergeable` form.
When doing this, care has to be taken to deep copy the value when
accessed, as it is modified in place before being updated in the store,
and accessed outside the store mutex.
Note a side effect of this change is that is no longer straightforward
to expose the `memberlist_kv_store_value_bytes` metric, as this reported
the size of the encoded data, therefore it has been removed.
Signed-off-by: Steve Simpson <steve.simpson@grafana.com>
Signed-off-by: Steve Simpson <steve.simpson@grafana.com>
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Manual tests results showed improved performances after this change, so let's get it merged. We can further re-iterate on follow up PRs. |
alvinlin123
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…xproject#4345) * Optimise memberlist kv store access by storing data unencoded. The following profile data was taken from running 50 idle ingesters with memberlist, with almost everything at default values (5s heartbeats): ``` 52.16% mergeBytesValueForKey +- 52.16% mergeValueForKey +- 47.84% computeNewValue +- 27.24% codec Proto Decode +- 26.25% mergeWithTime ``` It is apparent from the this that a lot of time is spent on the memberlist receive path, as might be expected, specifically, the merging of the update into the current state. The cost however is not in decoding the incoming states (occurs in `mergeBytesValueForKey` before `mergeValueForKey`), but in fact decoding _current state_ of the value in the store (as it is stored encoded). The ring state was measured at 123K (50 ingesters), so it makes sense that decoding could be costly. This can be avoided by storing the value in it's decoded `Mergeable` form. When doing this, care has to be taken to deep copy the value when accessed, as it is modified in place before being updated in the store, and accessed outside the store mutex. Note a side effect of this change is that is no longer straightforward to expose the `memberlist_kv_store_value_bytes` metric, as this reported the size of the encoded data, therefore it has been removed. Signed-off-by: Steve Simpson <steve.simpson@grafana.com> * Typo. Signed-off-by: Steve Simpson <steve.simpson@grafana.com> * Review comments. Signed-off-by: Steve Simpson <steve.simpson@grafana.com> Signed-off-by: Alvin Lin <alvinlin@amazon.com>
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What this PR does:
The following profile data was taken from running 50 idle ingesters with
memberlist, with almost everything at default values (5s heartbeats):
It is apparent from the this that a lot of time is spent on the memberlist
receive path, as might be expected, specifically, the merging of the update
into the current state. The cost however is not in decoding the incoming
states (occurs in
mergeBytesValueForKeybeforemergeValueForKey), butin fact decoding current state of the value in the store (as it is stored
encoded). The ring state was measured at 123K (50 ingesters), so it makes
sense that decoding could be costly.
This can be avoided by storing the value in it's decoded
Mergeableform.When doing this, care has to be taken to deep copy the value when
accessed, as it is modified in place before being updated in the store,
and accessed outside the store mutex.
Note a side effect of this change is that is no longer straightforward
to expose the
memberlist_kv_store_value_bytesmetric, as this reportedthe size of the encoded data, therefore it has been removed.
Checklist
Documentation addedCHANGELOG.mdupdated - the order of entries should be[CHANGE],[FEATURE],[ENHANCEMENT],[BUGFIX]