> On 4 May 2017 at 20:05, Magnus Hagander <mag...@hagander.net> wrote:
>
> PFA a patch that adds a new function, pg_move_replication_slot, that
makes it
> possible to move the location of a replication slot without actually
> consuming all the WAL on it.
Just a few questions just a few questions out of curiosity:
* does it make sense to create a few tests for this function in
`contrib/test_decoding` (as shown in attachment)?
* what should happen if the second argument is `NULL`? There is a
verification
`XLogRecPtrIsInvalid(moveto)`, but it's possible to pass `NULL`, and looks
like it leads to result different from boolean:
```
SELECT pg_move_replication_slot('regression_slot_5', NULL);
pg_move_replication_slot
--------------------------
(1 row)
```
diff --git a/contrib/test_decoding/expected/slot.out b/contrib/test_decoding/expected/slot.out
index 9f5f8a9..7c69110 100644
--- a/contrib/test_decoding/expected/slot.out
+++ b/contrib/test_decoding/expected/slot.out
@@ -101,3 +101,39 @@ SELECT pg_drop_replication_slot('regression_slot1');
ERROR: replication slot "regression_slot1" does not exist
SELECT pg_drop_replication_slot('regression_slot2');
ERROR: replication slot "regression_slot2" does not exist
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot_3', 'test_decoding');
+ ?column?
+----------
+ init
+(1 row)
+
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot_4', 'test_decoding', true);
+ ?column?
+----------
+ init
+(1 row)
+
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot_5', 'test_decoding');
+ ?column?
+----------
+ init
+(1 row)
+
+SELECT pg_move_replication_slot('regression_slot_3', '0/aabbccdd');
+ pg_move_replication_slot
+--------------------------
+ t
+(1 row)
+
+SELECT pg_move_replication_slot('regression_slot_4', '0/aabbccdd');
+ pg_move_replication_slot
+--------------------------
+ t
+(1 row)
+
+SELECT pg_move_replication_slot('regression_slot_5', NULL);
+ pg_move_replication_slot
+--------------------------
+
+(1 row)
+
diff --git a/contrib/test_decoding/sql/slot.sql b/contrib/test_decoding/sql/slot.sql
index fa9561f..207f845 100644
--- a/contrib/test_decoding/sql/slot.sql
+++ b/contrib/test_decoding/sql/slot.sql
@@ -53,3 +53,12 @@ SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot1', 'test_
-- both should error as they should be dropped on error
SELECT pg_drop_replication_slot('regression_slot1');
SELECT pg_drop_replication_slot('regression_slot2');
+
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot_3', 'test_decoding');
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot_4', 'test_decoding', true);
+
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot_5', 'test_decoding');
+
+SELECT pg_move_replication_slot('regression_slot_3', '0/aabbccdd');
+SELECT pg_move_replication_slot('regression_slot_4', '0/aabbccdd');
+SELECT pg_move_replication_slot('regression_slot_5', NULL);
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 6298657..d05974e 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -18986,6 +18986,24 @@ postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
be called when connected to the same database the slot was created on.
</entry>
</row>
+ <row>
+ <entry>
+ <indexterm>
+ <primary>pg_move_replication_slot</primary>
+ </indexterm>
+ <literal><function>pg_move_replication_slot(<parameter>slot_name</parameter> <type>name</type>, <parameter>position</parameter> <type>pg_lsn</type>)</function></literal>
+ </entry>
+ <entry>
+ <type>bool</type>
+ </entry>
+ <entry>
+ Moves the current restart position of a physical or logical
+ replication slot named <parameter>slot_name</parameter>.
+ The slot will not be moved backwards, and it will not be
+ moved beyond the current insert location. Returns true if
+ the position was changed.
+ </entry>
+ </row>
<row>
<entry>
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 6ee1e68..a9faa10 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -176,6 +176,66 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
}
/*
+ * SQL function for moving the position in a replication slot.
+ */
+Datum
+pg_move_replication_slot(PG_FUNCTION_ARGS)
+{
+ Name slotname = PG_GETARG_NAME(0);
+ XLogRecPtr moveto = PG_GETARG_LSN(1);
+ char *slotnamestr;
+ bool changed = false;
+ bool backwards = false;
+
+ Assert(!MyReplicationSlot);
+
+ check_permissions();
+
+ if (XLogRecPtrIsInvalid(moveto))
+ ereport(ERROR,
+ (errmsg("Invalid target xlog position ")));
+
+ /* Temporarily acquire the slot so we "own" it */
+ ReplicationSlotAcquire(NameStr(*slotname));
+
+ if (moveto > GetXLogWriteRecPtr())
+ /* Can't move past current position, so truncate there */
+ moveto = GetXLogWriteRecPtr();
+
+ /* Now adjust it */
+ SpinLockAcquire(&MyReplicationSlot->mutex);
+ if (MyReplicationSlot->data.restart_lsn != moveto)
+ {
+ /* Never move backwards, because bad things can happen */
+ if (MyReplicationSlot->data.restart_lsn > moveto)
+ backwards = true;
+ else
+ {
+ MyReplicationSlot->data.restart_lsn = moveto;
+ changed = true;
+ }
+ }
+ SpinLockRelease(&MyReplicationSlot->mutex);
+
+ if (backwards)
+ ereport(WARNING,
+ (errmsg("Not moving replication slot backwards!")));
+
+
+ if (changed)
+ {
+ ReplicationSlotMarkDirty();
+ ReplicationSlotsComputeRequiredLSN();
+ ReplicationSlotSave();
+ }
+
+ ReplicationSlotRelease();
+
+ PG_RETURN_BOOL(changed);
+}
+
+
+/*
* pg_get_replication_slots - SQL SRF showing active replication slots.
*/
Datum
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index 82562ad..04e97ff 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -5289,6 +5289,8 @@ DATA(insert OID = 3779 ( pg_create_physical_replication_slot PGNSP PGUID 12 1 0
DESCR("create a physical replication slot");
DATA(insert OID = 3780 ( pg_drop_replication_slot PGNSP PGUID 12 1 0 0 0 f f f f t f v u 1 0 2278 "19" _null_ _null_ _null_ _null_ _null_ pg_drop_replication_slot _null_ _null_ _null_ ));
DESCR("drop a replication slot");
+DATA(insert OID = 3998 ( pg_move_replication_slot PGNSP PGUID 12 1 0 0 0 f f f f t f v u 2 0 16 "19 3220" _null_ _null_ _null_ _null_ _null_ pg_move_replication_slot _null_ _null_ _null_ ));
+DESCR("move a replication slot position");
DATA(insert OID = 3781 ( pg_get_replication_slots PGNSP PGUID 12 1 10 0 0 f f f f f t s s 0 0 2249 "" "{19,19,25,26,16,16,23,28,28,3220,3220}" "{o,o,o,o,o,o,o,o,o,o,o}" "{slot_name,plugin,slot_type,datoid,temporary,active,active_pid,xmin,catalog_xmin,restart_lsn,confirmed_flush_lsn}" _null_ _null_ pg_get_replication_slots _null_ _null_ _null_ ));
DESCR("information about replication slots currently in use");
DATA(insert OID = 3786 ( pg_create_logical_replication_slot PGNSP PGUID 12 1 0 0 0 f f f f t f v u 3 0 2249 "19 19 16" "{19,19,16,25,3220}" "{i,i,i,o,o}" "{slot_name,plugin,temporary,slot_name,wal_position}" _null_ _null_ pg_create_logical_replication_slot _null_ _null_ _null_ ));
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