For old channels, this can take a while, and it stops everything. But
we are only doing this to save space; it's not a *functional* necessity.
A quick and dirty test with 50,000 htlcs shows the htlc deletion took
450msec. I tried adding an index, and changing it to set hstate to
HTLC_STATE_INVALID instead of deleting entries, but it still took about 350ms.
Whereas the "COUNT(*)" only took 1.7msec, so it's worth keeping.
Reported-by: @michael1011
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Changed: lightningd: we defer deletion of old htlcs on channel close, to avoid pausing for a long time (we clean them on startup)
Fixes: https://github.com/ElementsProject/lightning/issues/7962
cb2849d03f