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Use single map and remove_all for EventTopics
#4566
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shawntabrizi
added
A0-please_review
shawntabrizi
commented
Jan 8, 2020
| /// All topic vectors have deterministic storage locations depending on the topic. This | ||
| /// allows light-clients to leverage the changes trie storage tracking mechanism and | ||
| /// in case of changes fetch the list of events of interest. | ||
| /// | ||
| /// The value has the type `(T::BlockNumber, EventIndex)` because if we used only just | ||
| /// the `EventIndex` then in case if the topic has the same contents on the next block | ||
| /// no notification will be triggered thus the event might be lost. | ||
| EventTopics get(fn event_topics): double_map hasher(blake2_256) (), blake2_256(T::Hash) | ||
| => Vec<(T::BlockNumber, EventIndex)>; | ||
| EventTopics get(fn event_topics): map T::Hash => Vec<(T::BlockNumber, EventIndex)>; |
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We could reduce the complexity of the hasher used on the key here.
I don't quite understand if this is something worth changing.
bkchr
approved these changes
Jan 8, 2020
|
CC @jacogr |
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#2491 introduced light client friendly events.
It used a trick with the
double_mapapi where it was able to clear a single map by removing a single prefix of thedouble_map.See: paritytech/polkadot-sdk#371
Now that all storage items use
StoragePrefixedMap, we can now access theremove_allAPI directly from a single map.This updates the implementation of
EventTopicsto use a single map and theremove_allapi rather than thedouble_maphack.