Documentation
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Overview ¶
Package cache provides a cache of an event stream's most recent events.
Index ¶
Constants ¶
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Variables ¶
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Functions ¶
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Types ¶
type Cache ¶
type Cache struct {
// contains filtered or unexported fields
}
Cache holds the most recent events from one event stream that match a known set of message types.
The cache holds a contiguous segment of the stream, [begin, end), within which it holds every event of those types and no others, so the events it holds may have gaps between their offsets. The cache's segment ends where the last events appended to the cache ended, and begins after the last event that the cache evicted.
A cache has one writer, which resets it with Cache.Reset and appends to it with Cache.Append, and any number of readers, which observe its segment through Cache.Segment.
func New ¶
New returns an empty cache. It holds at most the given number of events, and its segment begins and ends at the given offset.
func (*Cache) Append ¶
func (c *Cache) Append(begin, end uint64, envelopes []*envelopepb.Envelope)
Append adds the events in the range [begin, end) of the stream to the cache.
The range must be contiguous with the cache's segment, so the given begin offset must be the offset at which that segment currently ends. The segment then extends to the given end offset.
If the cache is then over capacity, it evicts its oldest events, and its segment begins after the last of them.
Each envelope must have the envelopepb.EventStreamPosition extension set, and the envelopes must be in offset order.
type Relation ¶
type Relation int
Relation describes where a checkpoint lies in relation to a Segment.
Its values follow the convention of cmp.Compare: negative if the checkpoint is before the segment, zero if it is within it, and positive if it is after it.
const ( // Before means that the checkpoint is before the segment, so the events // from the checkpoint must be read from history. Before Relation = -1 // Within means that the checkpoint is inside the segment, so the segment // holds the events from the checkpoint. Within Relation = 0 // After means that the checkpoint is at or beyond the end of the segment, // so there is nothing to deliver until the cache is appended to past it. After Relation = +1 )
type Segment ¶
type Segment struct {
// Begin and End bound the segment, [Begin, End).
Begin, End uint64
// contains filtered or unexported fields
}
Segment is the segment of the stream that a Cache holds, as an immutable snapshot.
func (Segment) Read ¶
func (s Segment) Read( cp uint64, types *uuidcollection.Set, ) ([]*envelopepb.Envelope, Relation)
Read returns the events in the segment from the given checkpoint.
Only events of the given types are returned. It also returns where the checkpoint lies in relation to the segment, and the events are meaningful only if the checkpoint is Within it.
Source Files