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package raft
import (
"fmt"
"sync"
)
// LogCache wraps any LogStore implementation to provide an
// in-memory ring buffer. This is used to cache access to
// the recently written entries. For implementations that do not
// cache themselves, this can provide a substantial boost by
// avoiding disk I/O on recent entries.
type LogCache struct {
store LogStore
cache []*Log
l sync.RWMutex
}
// NewLogCache is used to create a new LogCache with the
// given capacity and backend store.
func NewLogCache(capacity int, store LogStore) (*LogCache, error) {
if capacity <= 0 {
return nil, fmt.Errorf("capacity must be positive")
}
c := &LogCache{
store: store,
cache: make([]*Log, capacity),
}
return c, nil
}
func (c *LogCache) GetLog(idx uint64, log *Log) error {
// Check the buffer for an entry
c.l.RLock()
cached := c.cache[idx%uint64(len(c.cache))]
c.l.RUnlock()
// Check if entry is valid
if cached != nil && cached.Index == idx {
*log = *cached
return nil
}
// Forward request on cache miss
return c.store.GetLog(idx, log)
}
func (c *LogCache) StoreLog(log *Log) error {
return c.StoreLogs([]*Log{log})
}
func (c *LogCache) StoreLogs(logs []*Log) error {
// Insert the logs into the ring buffer
c.l.Lock()
for _, l := range logs {
c.cache[l.Index%uint64(len(c.cache))] = l
}
c.l.Unlock()
return c.store.StoreLogs(logs)
}
func (c *LogCache) FirstIndex() (uint64, error) {
return c.store.FirstIndex()
}
func (c *LogCache) LastIndex() (uint64, error) {
return c.store.LastIndex()
}
func (c *LogCache) DeleteRange(min, max uint64) error {
// Invalidate the cache on deletes
c.l.Lock()
c.cache = make([]*Log, len(c.cache))
c.l.Unlock()
return c.store.DeleteRange(min, max)
}
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