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Filter out auth chain queries that don't exist #16552

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Nov 22, 2023
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Filter out auth chain queries that don't exist #16552

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71d8645
Exclude sending a database query that can't exist
realtyem Oct 25, 2023
98f253e
[REVERT] Add in metrics counter to prove this gets hit
realtyem Oct 25, 2023
76e2aca
changelog
realtyem Oct 26, 2023
5791fa2
Revert "[REVERT] Add in metrics counter to prove this gets hit"
realtyem Oct 26, 2023
08c27f0
Merge branch 'develop' into auth-chain-exclude-retrieving-nonexistent…
clokep Nov 16, 2023
21c44fc
Merge branch 'develop' into auth-chain-exclude-retrieving-nonexistent…
realtyem Nov 21, 2023
94e22c2
Just continue the for loop if the sequence number is 1, since that wi…
realtyem Nov 21, 2023
3eaeaff
Remove comment
realtyem Nov 22, 2023
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1 change: 1 addition & 0 deletions changelog.d/16552.misc
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Reduce a little database load while processing state auth chains.
5 changes: 5 additions & 0 deletions synapse/storage/databases/main/event_federation.py
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I agree that chain IDs are never 0. They come from a DB-backed sequence:

synapse/synapse/storage/databases/main/events_worker.py

Lines 293 to 300 in 12ca87f

self.event_chain_id_gen = build_sequence_generator(
db_conn,
database.engine,
get_chain_id_txn,
"event_auth_chain_id",
table="event_auth_chains",
id_column="chain_id",
)

synapse/synapse/storage/schema/main/delta/59/04_event_auth_chains.sql.postgres

Line 16 in 25f43fa

CREATE SEQUENCE IF NOT EXISTS event_auth_chain_id;

which per https://www.postgresql.org/docs/16/sql-createsequence.html#id-1.9.3.81.6 should start at 1 and increase by 1.

Therefore querying for events in chain 0 will never return anything.

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Oh, your point is that the sequence_number in the chains is never 0?

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It looks like these are also seeded at 1 and grow by 1:

synapse/synapse/storage/databases/main/events.py

Lines 941 to 950 in e9069c9

# We found a chain ID/sequence number candidate, check its
# not already taken.
proposed_new_id = existing_chain_id[0]
proposed_new_seq = existing_chain_id[1] + 1
if chain_to_max_seq_no[proposed_new_id] < proposed_new_seq:
new_chain_tuple = (
proposed_new_id,
proposed_new_seq,
)

Original file line number Diff line number Diff line change
Expand Up @@ -301,6 +301,11 @@ def _get_auth_chain_ids_using_cover_index_txn(
# Add the initial set of chains, excluding the sequence corresponding to
# initial event.
for chain_id, seq_no in event_chains.items():
# Check if the initial event is the first item in the chain. If so, then
# there is nothing new to add from this chain.
if seq_no == 1:
continue

chains[chain_id] = max(seq_no - 1, chains.get(chain_id, 0))

# Now for each chain we figure out the maximum sequence number reachable
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