@override

Return a mutable char* pointing to a string's internal buffer, which may not be null-terminated. Writing through this pointer will modify the string.

toString

写入数据 */

mutex hold

/////////////////////////

compact file(sstable) whoes filenumber is less than limit_filenumber and range is in [begin, end). Only compacting level 0 files output to level 1, fi

/////////////////////////////////// compact for repair

skip expired time

Return the current output pointer so that a caller can see how many bytes were produced. Note: this is not a Sink method.