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zhangwenjian
b4b5bc5b3a
One row per database, taken and renewed by single UPDATE statements whose RowsAffected the database decides. Nothing uses it yet; the scheduler is wired to it next. The two timestamps are epoch milliseconds in a BIGINT rather than timestamp columns, which is the one decision here worth explaining. A timestamp does not survive the trip through a driver unchanged: read over go-admin's own `parseTime=True&loc=Local` DSN, MySQL's UTC_TIMESTAMP arrives relabelled as local time, and on a UTC+8 host every lease is eight hours out. It is invisible to any test that compares the lease against itself, because each instance's own arithmetic stays self-consistent - only the comparison between two instances is wrong, which is the only comparison that matters. An integer has no timezone for a driver to apply. The migration seeds the row free. There is no insert path at runtime, so two instances starting together cannot race to create the row they are both trying to claim, and neither has to tell a duplicate-key error apart from a real one in whichever driver it is running against. A missing row is therefore reported rather than recovered from: silently never scheduling anywhere is the worse failure. The current-time expression differs per dialect and all four are covered: MySQL, PostgreSQL and SQL Server against real servers, SQLite by default.