56 lines
1.6 KiB
Ruby
56 lines
1.6 KiB
Ruby
module Carto
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module Db
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module MigrationHelper
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LOCK_TIMEOUT_MS = 1000
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MAX_RETRIES = 3
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WAIT_BETWEEN_RETRIES_S = 2
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def migration(up_block, down_block)
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Sequel.migration do
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# Forces this migration to run under a transaction (controlled by Sequel)
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transaction
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up do
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lock_safe_migration(&up_block)
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end
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down do
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lock_safe_migration(&down_block)
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end
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end
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end
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private
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def lock_safe_migration(&block)
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run "SET lock_timeout TO #{LOCK_TIMEOUT_MS}"
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# As the external transaction is controlled by Sequel, we cannot ROLLBACK and BEGIN a new one
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# Instead, we use SAVEPOINTs (https://www.postgresql.org/docs/current/static/sql-savepoint.html)
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# to start a "sub-transaction" that we can rollback without affecting Sequel
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run 'SAVEPOINT before_migration'
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(1..MAX_RETRIES).each do
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begin
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instance_eval &block
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return
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rescue Sequel::DatabaseError => e
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if e.message.include?('lock timeout')
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# In case of timeout, we retry by reexecuting the code since the SAVEPOINT
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run 'ROLLBACK TO SAVEPOINT before_migration'
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sleep WAIT_BETWEEN_RETRIES_S
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else
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puts e.message
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raise e
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end
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end
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end
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# Raising an exception forces Sequel to rollback the entire transaction
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raise 'Retries exceeded during database migration'
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ensure
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run "SET lock_timeout TO DEFAULT"
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end
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end
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end
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end
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