BlockIO

Block的输入输出, 主要有BlockInputStream 和 BlockOutputStream, 输入输出的基本单位为Block

getHeader header的作用是啥？表明data的schema吗?

IBlockInputStream

The stream interface for reading data by blocks from the database. Relational operations are supposed to be done also as implementations of this interface. Watches out at how the source of the blocks works. Lets you get information for profiling: rows per second, blocks per second, megabytes per second, etc. Allows you to stop reading data (in nested sources).

IBlockInputStream 主要接口 read, readPrefix, readSuffix

这个地方的limit, quta, 以及info之类的作用是什么?

IBlockInputStream 继承关系

AsynchronousBlockInputStream

Executes another BlockInputStream in a separate thread. This serves two purposes:

1. Allows you to make the different stages of the query execution pipeline work in parallel.
2. Allows you not to wait until the data is ready, and periodically check their readiness without blocking. This is necessary, for example, so that during the waiting period you can check if a packet has come over the network with a request to interrupt the execution of the query. It also allows you to execute multiple queries at the same time.

PipelineExecutingBlockInputStream

Implement IBlockInputStream from QueryPipeline. It's a temporary wrapper.

TODO:

1. TypePromotion 模板
2. Cow 模板

IBlockOutputStream

Interface of stream for writing data (into table, filesystem, network, terminal, etc.)