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b89e151054
This feature, building on previous commits, allows the write-ahead log stream to be decoded into a series of logical changes; that is, inserts, updates, and deletes and the transactions which contain them. It is capable of handling decoding even across changes to the schema of the effected tables. The output format is controlled by a so-called "output plugin"; an example is included. To make use of this in a real replication system, the output plugin will need to be modified to produce output in the format appropriate to that system, and to perform filtering. Currently, information can be extracted from the logical decoding system only via SQL; future commits will add the ability to stream changes via walsender. Andres Freund, with review and other contributions from many other people, including Álvaro Herrera, Abhijit Menon-Sen, Peter Gheogegan, Kevin Grittner, Robert Haas, Heikki Linnakangas, Fujii Masao, Abhijit Menon-Sen, Michael Paquier, Simon Riggs, Craig Ringer, and Steve Singer.
90 lines
2.2 KiB
Plaintext
90 lines
2.2 KiB
Plaintext
-- predictability
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SET synchronous_commit = on;
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-- fail because we're creating a slot while in an xact with xid
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BEGIN;
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SELECT txid_current() = 0;
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?column?
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----------
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f
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(1 row)
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SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
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ERROR: cannot create logical replication slot in transaction that has performed writes
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ROLLBACK;
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-- fail because we're creating a slot while in an subxact whose topxact has a xid
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BEGIN;
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SELECT txid_current() = 0;
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?column?
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----------
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f
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(1 row)
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SAVEPOINT barf;
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SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
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ERROR: cannot create logical replication slot in transaction that has performed writes
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ROLLBACK TO SAVEPOINT barf;
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ROLLBACK;
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-- succeed, outside tx.
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SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
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?column?
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----------
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init
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(1 row)
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SELECT 'stop' FROM pg_drop_replication_slot('regression_slot');
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?column?
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----------
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stop
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(1 row)
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-- succeed, in tx without xid.
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BEGIN;
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SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
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?column?
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----------
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init
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(1 row)
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COMMIT;
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CREATE TABLE nobarf(id serial primary key, data text);
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INSERT INTO nobarf(data) VALUES('1');
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-- decoding works in transaction with xid
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BEGIN;
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SELECT txid_current() = 0;
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?column?
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----------
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f
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(1 row)
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-- don't show yet, haven't committed
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INSERT INTO nobarf(data) VALUES('2');
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SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0');
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data
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-----------------------------------------------------------
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BEGIN
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COMMIT
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BEGIN
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table public.nobarf: INSERT: id[integer]:1 data[text]:'1'
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COMMIT
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(5 rows)
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COMMIT;
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INSERT INTO nobarf(data) VALUES('3');
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SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0');
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data
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-----------------------------------------------------------
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BEGIN
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table public.nobarf: INSERT: id[integer]:2 data[text]:'2'
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COMMIT
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BEGIN
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table public.nobarf: INSERT: id[integer]:3 data[text]:'3'
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COMMIT
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(6 rows)
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SELECT 'stop' FROM pg_drop_replication_slot('regression_slot');
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?column?
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----------
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stop
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(1 row)
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