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Zero-downtime
Postgres migrations -
the hard parts
@ChrisSinjo
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Apps change
frequently
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Many apps can’t
take downtime
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The easy parts
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- Multiple app versions
- Fast DDL statements
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Fine, until it’s not
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We took downtime :(
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Let’s talk about
queues
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-- Slow query (AccessShare)
SELECT DISTINCT(customer_id) FROM payments;
-- Forces this to queue (AccessExclusive)
ALTER TABLE payments
ADD COLUMN refunded boolean;
-- Which blocks these (AccessShare)
SELECT * FROM payments WHERE id = 123;
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- Kill slow queries
- Set lock_timeout low
- Enable log_lock_waits
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We blogged about this
two weeks ago
I’ll tweet the link from @ChrisSinjo