Remove four indexes from the invoices table that either duplicate existing
UNIQUE constraint indexes or are never used in WHERE clauses:
- invoices_hash_idx: redundant, UNIQUE constraint on hash already creates
an implicit index
- invoices_payment_addr_idx: redundant, UNIQUE constraint on payment_addr
already creates an implicit index
- invoices_preimage_idx: unused, preimage is NULL on all new invoices and
is never used as a query filter
- invoices_settled_at_idx: unused, settled_at is NULL on all pending
invoices and is never used as a query filter (settle_index is used
instead)
Dropping these reduces B-tree working set size, which improves page cache
utilization as the invoice table grows.
ziggie
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