Introduce the minimal storage scaffolding for the watchman module:
- db_set_blobvar / db_get_blobvar helpers for persisting binary
values (e.g. block hashes) in the SQL `vars` table.
- load_tip(): recover last_processed_height and last_processed_hash
from the wallet db.
- apply_rescan(): honour --rescan by adjusting the loaded tip
downward (negative = absolute height, positive = N blocks back).
- watchman_new(): allocate the struct, initialise the pending-op
array, and call load_tip + apply_rescan.
Wire the watchman field into struct lightningd via a forward
declaration; instantiation at startup lands in a later commit
along with the rest of the wiring.
We always start a transaction before processing, but there are cases where
we don't need to. Switch to doing it on-demand.
This doesn't make a big difference for sqlite3, but it can for Postgres because
of the latency: 12% or so. Every bit helps!
30 runs, min-max(mean+/-stddev):
Postgres before: 8.842773-9.769030(9.19531+/-0.21)
Postgres after: 8.007967-8.321856(8.14172+/-0.066)
sqlite3 before: 7.486042-8.371831(8.15544+/-0.19)
sqlite3 after: 7.973411-8.576135(8.3025+/-0.12)
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Put an assertion inside db.c, and run every command we do (in testing) through
a `check` variant.
I inserted a deliberate bug (made addpsbtoutput call wallet_get_newindex()
before returning when running `check`, and indeed, backtrace as expected.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
