Return the length (in bytes) of the referenced data

If another resource is available, acquire it and return true. Else return false.

从 background_work_queue_ 中取出一个任务并执行，由于任务队列并没有最大数量限制，所以不需要 * 在取出数据以后 notify 其它线程，一个很简易的实现 */

Determine if the CPU running this program can accelerate the CRC32C calculation.

返回 Block 未压缩之前的大小 */

Encode a suitable internal key target for "target" and return it. Uses *scratch as scratch space, and the returned pointer will point into this scratc

注意，该方法调用后 dst 指针将会向后移动 1~10 字节，具体取决于 varint 编码大小 */

Maximum number of bytes in all compacted files. We avoid expanding the lower level file set of a compaction if it would make the total compaction cov

Finds the largest key in a vector of files. Returns true if files it not empty. * 获取某一个 level 中最大的 InternalKey */

Finds minimum file b2=(l2, u2) in level file for which l2 > u1 and user_key(l2) = user_key(u1)

File descriptors are small non-negative integers. Returns void so the implementation can use ASSERT_EQ.

Finds an FD open since a previous call to GetOpenFileDescriptors(). |baseline_open_fds| is the result of a previous GetOpenFileDescriptors() call. As

Return the current manifest file number

Return the maximum number of concurrent mmaps.

Return the maximum number of concurrent mmaps.

Return the maximum number of read-only files to keep open.

Maximum size of files to build during this compaction.

Compaction 入口函数 */

Returns true iff some level needs a compaction.

Creates a SnapshotImpl and appends it to the end of the list.