53 lines
1.6 KiB
Markdown
53 lines
1.6 KiB
Markdown
# ADR 012: ABCI Events
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## Changelog
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- *2018-09-02* Remove ABCI errors component. Update description for events
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- *2018-07-12* Initial version
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## Context
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ABCI tags were first described in [ADR 002](https://github.com/tendermint/tendermint/blob/master/docs/architecture/adr-002-event-subscription.md).
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They are key-value pairs that can be used to index transactions.
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Currently, ABCI messages return a list of tags to describe an
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"event" that took place during the Check/DeliverTx/Begin/EndBlock,
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where each tag refers to a different property of the event, like the sending and receiving account addresses.
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Since there is only one list of tags, recording data for multiple such events in
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a single Check/DeliverTx/Begin/EndBlock must be done using prefixes in the key
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space.
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Alternatively, groups of tags that constitute an event can be separated by a
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special tag that denotes a break between the events. This would allow
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straightforward encoding of multiple events into a single list of tags without
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prefixing, at the cost of these "special" tags to separate the different events.
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TODO: brief description of how the indexing works
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## Decision
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Instead of returning a list of tags, return a list of events, where
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each event is a list of tags. This way we naturally capture the concept of
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multiple events happening during a single ABCI message.
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TODO: describe impact on indexing and querying
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## Status
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Proposed
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## Consequences
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### Positive
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- Ability to track distinct events separate from ABCI calls (DeliverTx/BeginBlock/EndBlock)
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- More powerful query abilities
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### Negative
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- More complex query syntax
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- More complex search implementation
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### Neutral
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