StorageMergeTree

什么是MergeTree？原理是啥？有啥优缺点

MergeTree存储结构需要对用户写入的数据做排序然后进行有序存储，数据有序存储带来两大核心优势：

struct

read

write

write 返回一个MergeTreeBlockOutputStream

WriteTempPart

mutate

mergeMutateTask

finalizeMutatedPart

Initialize and write to disk new part fields like checksums, columns,