Gossmap: compaction support #8869
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rustyrussell
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Not a complete decode, just the highlights (what channel was announced or updated, what node was announced). Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
It didn't do anything, since the dev_compact_gossip_store command was removed. When we make it do something, it crashes since old_len is 0: ``` gossipd: gossip_store_compact: bad version gossipd: FATAL SIGNAL 6 (version v25.12rc3-1-g9e6c715-modded) ... gossipd: backtrace: ./stdlib/abort.c:79 (__GI_abort) 0x7119bd8288fe gossipd: backtrace: ./assert/assert.c:96 (__assert_fail_base) 0x7119bd82881a gossipd: backtrace: ./assert/assert.c:105 (__assert_fail) 0x7119bd83b516 gossipd: backtrace: gossipd/gossip_store.c:52 (append_msg) 0x56294de240eb gossipd: backtrace: gossipd/gossip_store.c:358 (gossip_store_compact) 0x56294 gossipd: backtrace: gossipd/gossip_store.c:395 (gossip_store_new) 0x56294de24 gossipd: backtrace: gossipd/gossmap_manage.c:455 (setup_gossmap) 0x56294de255 gossipd: backtrace: gossipd/gossmap_manage.c:488 (gossmap_manage_new) 0x56294 gossipd: backtrace: gossipd/gossipd.c:400 (gossip_init) 0x56294de22de9 ``` Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Our poor scid generation clashes badly with simplified hashing (the next patch) leading to l1's startup time when using a generated map moving from 4 seconds to 14 seconds. Under CI it actually timed out several tests. Fixing our fake scids to be more "random" reduces it to 1.5 seconds. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
It's actually quite quick to load a cache-hot 308,874,377 byte gossip_store (normal -Og build), but perf does show time spent in siphash(), which is a bit overkill here, so drop that: Before: Time to load: 66718983-78037766(7.00553e+07+/-2.8e+06)nsec After: Time to load: 54510433-57991725(5.61457e+07+/-1e+06)nsec We could save maybe 10% more by disabling checksums, but having that assurance is nice. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
We also put this in the store_ended message, too: so you can tell if the equivalent_offset there really refers to this new entry (or if two or more rewrites have happened). Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This is the first record, and ignored by everything else. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
It's used by common/gossip_store.c, which is used by many things other than gossipd. This file belongs in common. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
gossmap doesn't care, so gossipd currently has to iterate through the store to find them at startup. Create a callback for gossipd to use instead. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This way gossmap_manage can decide when to compact. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
We now only need to walk it if we're doing an upgrade. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Changelog-Changed: `gossipd` no longer compacts gossip_store on startup (improving start times).
This saves gossipd from converting it: ``` lightningd-1 2026-02-02T00:50:49.505Z DEBUG gossipd: Time to convert version 14 store: 890 msec ``` Reducing node startup time from 1.4 seconds to 0.5 seconds. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This is the file responsible for all the writing, so it should be responsible for the rewriting if necessary (rather than gossmap_manage). Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
gossip_store.c uses this to avoid two reads, and we want to use it elsewhere too. Also fix old comment on gossip_store_readhdr(). Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
A new subprocess run by gossipd to create a compacted gossip store. It's pretty simple: a linear compaction of the file. Once it's done the amount it was told to, then gossipd waits until it completes the last bit. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This isn't called anywhere yet. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Changelog-Added: `gossipd` now uses a `lightning_gossip_compactd` helper to compact the gossip_store on demand, keeping it under about 210MB.
And tests! Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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We used to do compaction of the gossip store, but it was buggy. So now we do it on every startup (which is slow). Better is to do it when required, using a separate process.