// Adds a new change to a channel log.
func (db *Database) AddToChangeLog(channelName string, entry channels.LogEntry, parentRevID string) error {
if channelName == "*" && !EnableStarChannelLog {
return nil
}
var fullUpdate bool
var removedCount int
fullUpdateAttempts := 0
logDocID := channelLogDocID(channelName)
err := db.Bucket.WriteUpdate(logDocID, 0, func(currentValue []byte) ([]byte, walrus.WriteOptions, error) {
// (Be careful: this block can be invoked multiple times if there are races!)
// Should I do a full update of the change log, removing older entries to limit its size?
// This has to be done occasionaly, but it's slower than simply appending to it. This
// test is a heuristic that seems to strike a good balance in practice:
fullUpdate = AlwaysCompactChangeLog ||
(len(currentValue) > 20000 && (rand.Intn(100) < len(currentValue)/5000))
removedCount = 0
if len(currentValue) == 0 {
channelLog := channels.ChangeLog{}
channelLog.Add(entry)
return encodeChannelLog(&channelLog), walrus.Raw, nil
}
if fullUpdate {
fullUpdateAttempts++
var newValue bytes.Buffer
removedCount = channels.TruncateEncodedChangeLog(bytes.NewReader(currentValue),
MaxChangeLogLength-1, &newValue)
if removedCount > 0 {
entry.Encode(&newValue, parentRevID)
return newValue.Bytes(), walrus.Raw, nil
}
}
w := bytes.NewBuffer(make([]byte, 0, 50000))
entry.Encode(w, parentRevID)
currentValue = append(currentValue, w.Bytes()...)
return currentValue, walrus.Raw, nil
})
/*if fullUpdate {
base.Log("Removed %d entries from %q", removedCount, channelName)
} else if fullUpdateAttempts > 0 {
base.Log("Attempted to remove entries %d times but failed", fullUpdateAttempts)
}*/
return err
}
// Writes new changes to my channel log document.
func (c *channelLogWriter) addToChangeLog_(entries []*changeEntry) {
var err error
dbExpvars.Add("channelLogAdds", 1)
logDocID := channelLogDocID(c.channelName)
// A fraction of the time we will do a full update and clean stuff out.
fullUpdate := AlwaysCompactChangeLog || len(entries) > MaxChangeLogLength/2 || rand.Intn(MaxChangeLogLength/len(entries)) == 0
if !fullUpdate {
// Non-full update; just append the new entries:
w := bytes.NewBuffer(make([]byte, 0, 100*len(entries)))
for _, entry := range entries {
entry.logEntry.Encode(w, entry.parentRevID)
}
data := w.Bytes()
err = c.bucket.Append(logDocID, data)
if err == nil {
base.LogTo("ChannelLog", "Appended %d sequence(s) to %q", len(entries), c.channelName)
dbExpvars.Add("channelLogAppends", 1)
} else if base.IsDocNotFoundError(err) {
// Append failed due to doc not existing, so fall back to full update
err = nil
fullUpdate = true
} else {
base.Warn("Error appending to %q -- %v", len(entries), c.channelName, err)
}
}
if fullUpdate {
// Full update: do a CAS-based read+write:
fullUpdateAttempts := 0
var oldChangeLogCount, newChangeLogCount int
err = c.bucket.WriteUpdate(logDocID, 0, func(currentValue []byte) ([]byte, walrus.WriteOptions, error) {
fullUpdateAttempts++
numToKeep := MaxChangeLogLength - len(entries)
if len(currentValue) == 0 || numToKeep <= 0 {
// If log was missing or empty, or will be entirely overwritten, create a new one:
entriesToWrite := entries
if numToKeep < 0 {
entriesToWrite = entries[-numToKeep:]
}
channelLog := channels.ChangeLog{}
for _, entry := range entriesToWrite {
channelLog.Add(*entry.logEntry)
}
newChangeLogCount = len(entriesToWrite)
oldChangeLogCount = newChangeLogCount
return encodeChannelLog(&channelLog), walrus.Raw, nil
} else {
// Append to an already existing change log:
var newValue bytes.Buffer
var nRemoved int
nRemoved, newChangeLogCount = channels.TruncateEncodedChangeLog(
bytes.NewReader(currentValue), numToKeep, numToKeep/2, &newValue)
for _, entry := range entries {
entry.logEntry.Encode(&newValue, entry.parentRevID)
}
oldChangeLogCount = nRemoved + newChangeLogCount
newChangeLogCount += len(entries)
return newValue.Bytes(), walrus.Raw, nil
}
})
if err == nil {
dbExpvars.Add("channelLogRewrites", 1)
dbExpvars.Add("channelLogRewriteCollisions", int64(fullUpdateAttempts-1))
base.LogTo("ChannelLog", "Wrote %d sequences (was %d now %d) to %q in %d attempts",
len(entries), oldChangeLogCount, newChangeLogCount, c.channelName, fullUpdateAttempts)
} else {
base.Warn("Error writing %d sequence(s) to %q -- %v", len(entries), c.channelName, err)
}
}
}