DioCrafts
29 lines
2.0 KiB
SQL
29 lines
2.0 KiB
SQL
-- no-transaction
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-- Paginated admin user listings sort newest-first with `id` as a stable
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-- tiebreaker. PostgreSQL 13+ uses this timestamp index plus an incremental
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-- sort only within equal-timestamp groups. Without the index,
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-- PostgreSQL scans and top-N sorts the entire user directory for every page.
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-- Keep the index narrow: the compact response fetches at most 500 heap rows,
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-- while INCLUDE-ing profile columns would bloat both RAM and write I/O.
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-- The initial 500k-row fixture with 100-way timestamp ties was superseded for
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-- resource accounting because B-tree posting-list dedup compressed its keys.
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-- Three independent representative A/B transactions (15 samples/shape, common
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-- UUID PK) measured mostly-unique timestamps at 11,255,808 bytes and +0.680 us
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-- per inserted user; first/deep pages improved 266.13x/24.21x. Ten-user bursts
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-- used 4,751,360 bytes and +0.582 us/user, improving reads 321.57x/18.29x.
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-- (`tools/perf-audit/admin_user_order_index_representative.sql`). The user
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-- explicitly accepted those corrected costs. This migration deliberately
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-- remains one-column. A later isolated representative A/B/C gate rejected the
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-- compound index: it regressed the common unique-timestamp first page by 6.45%,
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-- increased index bytes by 80.13%-327.76%, and added 0.445 us/user to burst
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-- inserts despite improving deep pages by 1.63x-2.30x.
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-- Build online: a regular CREATE INDEX would block INSERT/UPDATE/DELETE on
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-- auth.users (including the last_login_at write) for the full build. Keep this
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-- as the migration's only statement: PostgreSQL wraps multiple statements from
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-- one simple-query message in an implicit transaction, where CONCURRENTLY is
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-- forbidden. If a failed build leaves this name INVALID, operators must run
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-- `DROP INDEX CONCURRENTLY auth.idx_users_created_at_desc` before retrying;
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-- deliberately omit IF NOT EXISTS so an invalid index is never accepted.
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CREATE INDEX CONCURRENTLY idx_users_created_at_desc
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ON auth.users (created_at DESC);
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