Class Decoder

runtime/Log.h:844–904

* Encapsulates the knowledge for interpreting a compressed file produced * by an Encoder and producing a human-readable representation of the log * file. The Encoder class is intended to be reused as it maintains * fairly large data structures to hold fragments of the compressed logs. */

     * fairly large data structures to hold fragments of the compressed logs.
     */
    class Decoder {
    public:
        Decoder();
        ~Decoder();

        bool open(const char *filename);

        int64_t decompressUnordered(FILE *outputFd);
        int64_t decompressTo(FILE *outputFd);

        bool getNextLogStatement(LogMessage &logMsg,
                                 FILE *outputFd= nullptr);

    PRIVATE:
        /**
         * Reads and stores a BufferExtent from the compressed log and
         * facilitates the interpretation of the log messages contained in the
         * extent.
         */
        struct BufferFragment {
            // Stores the bytes in a compressed log BufferExtent. The size is
            // chosen to be a little bigger than the size of a runtime
            // StagingBuffer to account for any other entries that may be
            // inserted at runtime.
            char storage[NanoLogConfig::STAGING_BUFFER_SIZE
                                             + BufferExtent::maxSizeOfHeader()];

            // Number of valid bytes in storage.
            uint64_t validBytes;

            // The runtime StagingBuffer id associated with this extent.
            uint32_t runtimeId;

            // For efficient IO, we read the entire fragment in once and then
            // keep track of a read position within the buffer
            const char *readPos;

            // Marks the first invalid byte in storage
            char *endOfBuffer;

            // Indicates if there are more log messages that can be decompressed
            bool hasMoreLogs;

            // For sorting, store the metadata for the next log message to be
            // decompressed so we can access its absolute rdtsc timestamp.
            uint32_t nextLogId;
            uint64_t nextLogTimestamp;

            BufferFragment();
            void reset();
            bool hasNext();
            bool readBufferExtent(FILE *fd, bool *wrapAround=nullptr);
            bool decompressNextLogStatement(FILE *outputFd,
                                 uint64_t &logMsgsProcessed,
                                 LogMessage &logArguments,
                                 const Checkpoint &checkpoint,
                                 std::vector<void*>& fmtId2metadata,
                                 long aggregationFilterId=-1,