Major Description
A new scanner API for reducing unnecessary RPC calls:
Motivation:
- RPC is expensive to both client and server.
- The most important function for scanning is getting data, but for each scanning process within a region, there are 3 times of RPC that doesn't transfer data: open, last next, and close, I want to remove them all (for most of the situation)
Solution:
- a new scanner API (scanOpen) which has an option of transfer data along with the scannerID back in this call
- a new scanner API (scanNext) which is similar to current next, but returns flags of whether more data is available and whether need to scan next region. If no data left, automatically close the scanner.
- scanClose is still useful when you want to close the scanner before reach the end.
For most of the meta-scan, only one RPC will fetch all lines.