Allow to reset the chain to a particular block

[tomusdrw]

Re-syncing archive nodes is not always feasible nowadays. And sometimes due to bugs your DB might be missing or have incorrect values for Parity-generated data (think traces, fatdb, logs).
It should be possible (and easy) to re-sync the chain from some particular block to re-produce those values.
If I'm not mistaken, for archive nodes it's just a matter of reseting best block hash if "best" key of EXTRA column in DB.

EDIT:
Seems that sync/src/block_sync.rs will never attempt to import blocks that are already known, so reset requires to remove hashes of all previously imported blocks as well.

[mg6maciej]

Hey,
I've tried to do this on my own, connecting to RocksDB and changing the data.
Here are the steps I followed:

• sudo docker run -v /Users/mg6maciej/parityroot9:/storage parity/parity:v1.10.0 --base-path /storage --pruning archive --tracing 'on'
• wait a bit to synchronize a few blocks

...
2018-04-12 12:48:17 UTC Syncing  #463680 b5c4…fd25   593 blk/s  928 tx/s  31 Mgas/s  13660+    5 Qed   #477353   19/25 peers      9 MiB chain    6 MiB db   27 MiB queue   11 MiB sync  RPC:  0 conn,  0 req/s,   0 µs
2018-04-12 12:48:27 UTC Syncing  #469406 8a5f…614c   572 blk/s  804 tx/s  29 Mgas/s  16071+  116 Qed   #485604   20/25 peers      8 MiB chain    6 MiB db   33 MiB queue    9 MiB sync  RPC:  0 conn,  0 req/s,   0 µs

• Stop parity

^C2018-04-12 12:48:30 UTC Finishing work, please wait...

• Read the newest block from RocksDB best key in HEADERS (col3)
  c9919ded297babe7c21d4dd64ab76916a00b2e596657ad09411fea8cce032343, which corresponds to block number 470_558
• Set best to has corresponding to 450_000 (a1601b0a9b2e062ea358f09653c0b366380207bf544b5946b03ca2d4387ca17b)
• Delete all keys in HEADERS, BODIES and EXTRA (col1, col2 and col3) equal to hashes corresponding to blocks from 450_001 to 470_558. Note: in EXTRA these keys are prefixed with byte 0.
• Start parity with the same params as in step 1
• Be sad about the error "Parent not found"

2018-04-12 13:03:27 UTC Block import failed for #450002 (3716…00d5): Parent not found (a9f3…8123)
2018-04-12 13:03:30 UTC Public node URL: enode://3f50779cf8797326338ec05f6f455664ce71747e01de0a3f56e12c127d229f015b1985487dd1ad7fdf970da7d92f346810024fe85b65870a9bc1264592137940@172.17.0.2:30303
2018-04-12 13:03:36 UTC Syncing  #450000 a160…a17b     0 blk/s    0 tx/s   0 Mgas/s      0+    0 Qed   #449937    9/25 peers     74 KiB chain  0 bytes db  0 bytes queue  584 KiB sync  RPC:  0 conn,  0 req/s,   0 µs
2018-04-12 13:03:46 UTC Syncing  #450000 a160…a17b     0 blk/s    0 tx/s   0 Mgas/s      0+    0 Qed   #449873    2/25 peers     74 KiB chain  0 bytes db  0 bytes queue    2 MiB sync  RPC:  0 conn,  0 req/s,   0 µs
2018-04-12 13:03:55 UTC Syncing  #450000 a160…a17b     0 blk/s    0 tx/s   0 Mgas/s      0+    0 Qed   #449745    2/25 peers     74 KiB chain  0 bytes db  0 bytes queue    2 MiB sync  RPC:  0 conn,  0 req/s,   0 µs
2018-04-12 13:04:00 UTC Syncing  #450000 a160…a17b     0 blk/s    0 tx/s   0 Mgas/s      0+    0 Qed   #449745    2/25 peers     74 KiB chain  0 bytes db  0 bytes queue    2 MiB sync  RPC:  0 conn,  0 req/s,   0 µs
2018-04-12 13:04:05 UTC Syncing  #450000 a160…a17b     0 blk/s    0 tx/s   0 Mgas/s      0+    0 Qed   #449872    2/25 peers     74 KiB chain  0 bytes db  0 bytes queue    2 MiB sync  RPC:  0 conn,  0 req/s,   0 µs
2018-04-12 13:04:10 UTC Syncing  #450000 a160…a17b     0 blk/s    0 tx/s   0 Mgas/s      0+    0 Qed   #449999    2/25 peers     74 KiB chain  0 bytes db  0 bytes queue    2 MiB sync  RPC:  0 conn,  0 req/s,   0 µs

Is there anything else I need to delete for this to work? We want to reset Parity to block 5_200_000 as we noticed no logs returned for a couple of days in blocks from a month ago.

[richardpringle]

docs?