Add facility to copy replication slots

This allows the user to create duplicates of existing replication slots,
either logical or physical, and even changing properties such as whether
they are temporary or the output plugin used.

There are multiple uses for this, such as initializing multiple replicas
using the slot for one base backup; when doing investigation of logical
replication issues; and to select a different output plugins.

Author: Masahiko Sawada
Reviewed-by: Michael Paquier, Andres Freund, Petr Jelinek
Discussion: https://postgr.es/m/CAD21AoAm7XX8y_tOPP6j4Nzzch12FvA1wPqiO690RCk+uYVstg@mail.gmail.com

1 files changed, 94 insertions, 0 deletions

diff --git a/contrib/test_decoding/sql/slot.sql b/contrib/test_decoding/sql/slot.sql
index c8d08f85417..6d83fb26782 100644
--- a/contrib/test_decoding/sql/slot.sql
+++ b/contrib/test_decoding/sql/slot.sql
@@ -76,3 +76,97 @@ SELECT slot_name FROM pg_create_physical_replication_slot('regression_slot3');
 SELECT pg_replication_slot_advance('regression_slot3', '0/0'); -- invalid LSN
 SELECT pg_replication_slot_advance('regression_slot3', '0/1'); -- error
 SELECT pg_drop_replication_slot('regression_slot3');
+
+--
+-- Test copy functions for logical replication slots
+--
+
+-- Create and copy logical slots
+SELECT 'init' FROM pg_create_logical_replication_slot('orig_slot1', 'test_decoding', false);
+SELECT 'copy' FROM pg_copy_logical_replication_slot('orig_slot1', 'copied_slot1_no_change');
+SELECT 'copy' FROM pg_copy_logical_replication_slot('orig_slot1', 'copied_slot1_change_plugin', false, 'pgoutput');
+SELECT 'copy' FROM pg_copy_logical_replication_slot('orig_slot1', 'copied_slot1_change_plugin_temp', true, 'pgoutput');
+
+-- Check all copied slots status
+SELECT
+    o.slot_name, o.plugin, o.temporary, c.slot_name, c.plugin, c.temporary
+FROM
+    (SELECT * FROM pg_replication_slots WHERE slot_name LIKE 'orig%') as o
+    LEFT JOIN pg_replication_slots as c ON o.restart_lsn = c.restart_lsn  AND o.confirmed_flush_lsn = c.confirmed_flush_lsn
+WHERE
+    o.slot_name != c.slot_name
+ORDER BY o.slot_name, c.slot_name;
+
+-- Now we have maximum 4 replication slots. Check slots are properly
+-- released even when raise error during creating the target slot.
+SELECT 'copy' FROM pg_copy_logical_replication_slot('orig_slot1', 'failed'); -- error
+
+-- temporary slots were dropped automatically
+SELECT pg_drop_replication_slot('orig_slot1');
+SELECT pg_drop_replication_slot('copied_slot1_no_change');
+SELECT pg_drop_replication_slot('copied_slot1_change_plugin');
+
+-- Test based on the temporary logical slot
+SELECT 'init' FROM pg_create_logical_replication_slot('orig_slot2', 'test_decoding', true);
+SELECT 'copy' FROM pg_copy_logical_replication_slot('orig_slot2', 'copied_slot2_no_change');
+SELECT 'copy' FROM pg_copy_logical_replication_slot('orig_slot2', 'copied_slot2_change_plugin', true, 'pgoutput');
+SELECT 'copy' FROM pg_copy_logical_replication_slot('orig_slot2', 'copied_slot2_change_plugin_temp', false, 'pgoutput');
+
+-- Check all copied slots status
+SELECT
+    o.slot_name, o.plugin, o.temporary, c.slot_name, c.plugin, c.temporary
+FROM
+    (SELECT * FROM pg_replication_slots WHERE slot_name LIKE 'orig%') as o
+    LEFT JOIN pg_replication_slots as c ON o.restart_lsn = c.restart_lsn  AND o.confirmed_flush_lsn = c.confirmed_flush_lsn
+WHERE
+    o.slot_name != c.slot_name
+ORDER BY o.slot_name, c.slot_name;
+
+-- Cannot copy a logical slot to a physical slot
+SELECT 'copy' FROM pg_copy_physical_replication_slot('orig_slot2', 'failed'); -- error
+
+-- temporary slots were dropped automatically
+SELECT pg_drop_replication_slot('copied_slot2_change_plugin_temp');
+
+--
+-- Test copy functions for physical replication slots
+--
+
+-- Create and copy physical slots
+SELECT 'init' FROM pg_create_physical_replication_slot('orig_slot1', true);
+SELECT 'init' FROM pg_create_physical_replication_slot('orig_slot2', false);
+SELECT 'copy' FROM pg_copy_physical_replication_slot('orig_slot1', 'copied_slot1_no_change');
+SELECT 'copy' FROM pg_copy_physical_replication_slot('orig_slot1', 'copied_slot1_temp', true);
+
+-- Check all copied slots status. Since all slots don't reserve WAL we check only other fields.
+SELECT slot_name, slot_type, temporary FROM pg_replication_slots;
+
+-- Cannot copy a physical slot to a logical slot
+SELECT 'copy' FROM pg_copy_logical_replication_slot('orig_slot1', 'failed'); -- error
+
+-- Cannot copy a physical slot that doesn't reserve WAL
+SELECT 'copy' FROM pg_copy_physical_replication_slot('orig_slot2', 'failed'); -- error
+
+-- temporary slots were dropped automatically
+SELECT pg_drop_replication_slot('orig_slot1');
+SELECT pg_drop_replication_slot('orig_slot2');
+SELECT pg_drop_replication_slot('copied_slot1_no_change');
+
+-- Test based on the temporary physical slot
+SELECT 'init' FROM pg_create_physical_replication_slot('orig_slot2', true, true);
+SELECT 'copy' FROM pg_copy_physical_replication_slot('orig_slot2', 'copied_slot2_no_change');
+SELECT 'copy' FROM pg_copy_physical_replication_slot('orig_slot2', 'copied_slot2_notemp', false);
+
+-- Check all copied slots status
+SELECT
+    o.slot_name, o.temporary, c.slot_name, c.temporary
+FROM
+    (SELECT * FROM pg_replication_slots WHERE slot_name LIKE 'orig%') as o
+    LEFT JOIN pg_replication_slots as c ON o.restart_lsn = c.restart_lsn
+WHERE
+    o.slot_name != c.slot_name
+ORDER BY o.slot_name, c.slot_name;
+
+SELECT pg_drop_replication_slot('orig_slot2');
+SELECT pg_drop_replication_slot('copied_slot2_no_change');
+SELECT pg_drop_replication_slot('copied_slot2_notemp');