load csv progress notes

gistfile1.txt

For local:

First phase is all of total progress. Initial, simple, implementation is to count the number of files (N), each file, after being converted to KVs, counts for 1/N of this phase's progress. Follow up work to get the file size from the export storage. Then progress for this phase is number of bytes processed / total number of bytes (among all files).

For distributed:

Sampling phase is 1/3 of total progress. Same deal as local with counting files and then file sizes for progress, also keeping track of number of KVs produced.

Second phase is 1/3 of total progress. As KVs are consumed and written to RocksDB, progress is total number of written KVs / total number of KVs (among all distsql processors).

Third phase is 1/3 of total progress. Each SST written to storage is 1/N of this phase.