More debug interfaces for troubleshooting

When doing troubleshooting for https://github.com/pingcap/tics/issues/2756, these tools are very helpful:

• A tool for comparing the result from TiKV to TiFlash, finding out the rowkey(s)/Region(s) that is inconsistent
  • @JinheLin has implemented a prototype for it, but it only supports finding one different rowkey for non-clustered table
  • Locating by select count(*) from <table> where <min-key> <= _tidb_rowid and _tidb_rowid < <max-key>;
  • Setting set tidb_allow_batch_cop =0; and set tidb_allow_mpp = 0; would be helpful for locating the inconsistent rows
  • Need retry for checking multiple replicas
  • Locating the Region instead of rowkey would be greatly helpful
• TiFlash provides a debug interface for showing the overlapped between Regions and Segments
• TiFlash provides a debug interface for showing the details of stable and delta layer
  • Stable: the DTFile(s)
  • Delta: the type, id of DeltaPacks

These tools maybe helpful for troubleshooting:

• https://github.com/disksing/mok encoding table id & rowkey into Region key / decoding Region key into table id & rowkey
• pd-ctl doc
  • Find out all TiFlash stores: store --jq='.stores[].store | select(.labels | length>0 and contains([{"key":"engine","value":"tiflash"}])) | { id, address, state_name}'
  • Locate Region by key: region key <key>
  • Remove the Region peer: operator add remove-peer <region-id> <store-id>
• Dump the Regions of a table inside one TiFlash node:./bin/tiflash/tiflash client --host <tiflash-ip> --port <tiflash-tcp-port> --query "DBGInvoke dump_all_region(<table-id>)"

Need further investigation:

• Can PD locate the Region IDs by a key range?

Start with the prototype mentioned in the issue, the linked troubleshooting issue 2756, and the pd-ctl commands plus the TiFlash client DBGInvoke dump_all_region entry point. Investigate how to compare TiKV and TiFlash results, locate Regions, and expose Region/Segment and stable/delta details. Done should mean the needed troubleshooting interfaces support the listed replica, row, Region, and storage-layer cases.