private synchronized LogWriter getLogWriter(LogMessage m) throws IOException {
        Integer slot = dateHash(m.getTimestamp().toEpochMilli());
        LogWriter logWriter = logWriterLRUCache.get(slot);
        if (logWriter != null) {
            return logWriter;
        }

        // invariant: LogWriter we sought was not in the cache
        logWriter = new LogWriter(getPrefix(m), maxFileSize, filesArchived);
        logWriterLRUCache.put(slot, logWriter);

        return logWriter;
    }
Return the appropriate LogWriter given a log message.
logserver/src/main/java/com/yahoo/logserver/handlers/archive/ArchiverHandler.java