/*
* Find a previously created slot and mark it as used by this backend.
*/
void
ReplicationSlotAcquire(const char *name)
{
ReplicationSlot *slot = NULL;
int i;
int active_pid = 0;
Assert(MyReplicationSlot == NULL);
ReplicationSlotValidateName(name, ERROR);
/* Search for the named slot and mark it active if we find it. */
LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
for (i = 0; i < max_replication_slots; i++)
{
ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
if (s->in_use && strcmp(name, NameStr(s->data.name)) == 0)
{
volatile ReplicationSlot *vslot = s;
SpinLockAcquire(&s->mutex);
active_pid = vslot->active_pid;
if (active_pid == 0)
vslot->active_pid = MyProcPid;
SpinLockRelease(&s->mutex);
slot = s;
break;
}
}
LWLockRelease(ReplicationSlotControlLock);
/* If we did not find the slot or it was already active, error out. */
if (slot == NULL)
ereport(ERROR,
(errcode(ERRCODE_UNDEFINED_OBJECT),
errmsg("replication slot \"%s\" does not exist", name)));
if (active_pid != 0)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_IN_USE),
errmsg("replication slot \"%s\" is already active for pid %d",
name, active_pid)));
/* We made this slot active, so it's ours now. */
MyReplicationSlot = slot;
}
/*
* Create a new replication slot and mark it as used by this backend.
*
* name: Name of the slot
* db_specific: logical decoding is db specific; if the slot is going to
* be used for that pass true, otherwise false.
*/
void
ReplicationSlotCreate(const char *name, bool db_specific,
ReplicationSlotPersistency persistency)
{
ReplicationSlot *slot = NULL;
int i;
Assert(MyReplicationSlot == NULL);
ReplicationSlotValidateName(name, ERROR);
/*
* If some other backend ran this code concurrently with us, we'd likely
* both allocate the same slot, and that would be bad. We'd also be at
* risk of missing a name collision. Also, we don't want to try to create
* a new slot while somebody's busy cleaning up an old one, because we
* might both be monkeying with the same directory.
*/
LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
/*
* Check for name collision, and identify an allocatable slot. We need to
* hold ReplicationSlotControlLock in shared mode for this, so that nobody
* else can change the in_use flags while we're looking at them.
*/
LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
for (i = 0; i < max_replication_slots; i++)
{
ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
if (s->in_use && strcmp(name, NameStr(s->data.name)) == 0)
ereport(ERROR,
(errcode(ERRCODE_DUPLICATE_OBJECT),
errmsg("replication slot \"%s\" already exists", name)));
if (!s->in_use && slot == NULL)
slot = s;
}
LWLockRelease(ReplicationSlotControlLock);
/* If all slots are in use, we're out of luck. */
if (slot == NULL)
ereport(ERROR,
(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
errmsg("all replication slots are in use"),
errhint("Free one or increase max_replication_slots.")));
/*
* Since this slot is not in use, nobody should be looking at any part of
* it other than the in_use field unless they're trying to allocate it.
* And since we hold ReplicationSlotAllocationLock, nobody except us can
* be doing that. So it's safe to initialize the slot.
*/
Assert(!slot->in_use);
Assert(slot->active_pid == 0);
/* first initialize persistent data */
memset(&slot->data, 0, sizeof(ReplicationSlotPersistentData));
StrNCpy(NameStr(slot->data.name), name, NAMEDATALEN);
slot->data.database = db_specific ? MyDatabaseId : InvalidOid;
slot->data.persistency = persistency;
/* and then data only present in shared memory */
slot->just_dirtied = false;
slot->dirty = false;
slot->effective_xmin = InvalidTransactionId;
slot->effective_catalog_xmin = InvalidTransactionId;
slot->candidate_catalog_xmin = InvalidTransactionId;
slot->candidate_xmin_lsn = InvalidXLogRecPtr;
slot->candidate_restart_valid = InvalidXLogRecPtr;
slot->candidate_restart_lsn = InvalidXLogRecPtr;
/*
* Create the slot on disk. We haven't actually marked the slot allocated
* yet, so no special cleanup is required if this errors out.
*/
CreateSlotOnDisk(slot);
/*
* We need to briefly prevent any other backend from iterating over the
* slots while we flip the in_use flag. We also need to set the active
* flag while holding the ControlLock as otherwise a concurrent
* SlotAcquire() could acquire the slot as well.
*/
LWLockAcquire(ReplicationSlotControlLock, LW_EXCLUSIVE);
slot->in_use = true;
/* We can now mark the slot active, and that makes it our slot. */
SpinLockAcquire(&slot->mutex);
Assert(slot->active_pid == 0);
slot->active_pid = MyProcPid;
SpinLockRelease(&slot->mutex);
MyReplicationSlot = slot;
LWLockRelease(ReplicationSlotControlLock);
/*
* Now that the slot has been marked as in_use and active, it's safe to
* let somebody else try to allocate a slot.
*/
LWLockRelease(ReplicationSlotAllocationLock);
/* Let everybody know we've modified this slot */
ConditionVariableBroadcast(&slot->active_cv);
}
/*
* Permanently drop replication slot identified by the passed in name.
*/
void
ReplicationSlotDrop(const char *name)
{
ReplicationSlot *slot = NULL;
int i;
bool active;
char path[MAXPGPATH];
char tmppath[MAXPGPATH];
ReplicationSlotValidateName(name, ERROR);
/*
* If some other backend ran this code currently with us, we might both
* try to free the same slot at the same time. Or we might try to delete
* a slot with a certain name while someone else was trying to create a
* slot with the same name.
*/
LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
/* Search for the named slot and mark it active if we find it. */
LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
for (i = 0; i < max_replication_slots; i++)
{
ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
if (s->in_use && strcmp(name, NameStr(s->data.name)) == 0)
{
volatile ReplicationSlot *vslot = s;
SpinLockAcquire(&s->mutex);
active = vslot->active;
vslot->active = true;
SpinLockRelease(&s->mutex);
slot = s;
break;
}
}
LWLockRelease(ReplicationSlotControlLock);
/* If we did not find the slot or it was already active, error out. */
if (slot == NULL)
ereport(ERROR,
(errcode(ERRCODE_UNDEFINED_OBJECT),
errmsg("replication slot \"%s\" does not exist", name)));
if (active)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_IN_USE),
errmsg("replication slot \"%s\" is already active", name)));
/* Generate pathnames. */
sprintf(path, "pg_replslot/%s", NameStr(slot->data.name));
sprintf(tmppath, "pg_replslot/%s.tmp", NameStr(slot->data.name));
/*
* Rename the slot directory on disk, so that we'll no longer recognize
* this as a valid slot. Note that if this fails, we've got to mark the
* slot inactive again before bailing out.
*/
if (rename(path, tmppath) != 0)
{
volatile ReplicationSlot *vslot = slot;
SpinLockAcquire(&slot->mutex);
vslot->active = false;
SpinLockRelease(&slot->mutex);
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not rename \"%s\" to \"%s\": %m",
path, tmppath)));
}
/*
* We need to fsync() the directory we just renamed and its parent to make
* sure that our changes are on disk in a crash-safe fashion. If fsync()
* fails, we can't be sure whether the changes are on disk or not. For
* now, we handle that by panicking; StartupReplicationSlots() will
* try to straighten it out after restart.
*/
START_CRIT_SECTION();
fsync_fname(tmppath, true);
fsync_fname("pg_replslot", true);
END_CRIT_SECTION();
/*
* The slot is definitely gone. Lock out concurrent scans of the array
* long enough to kill it. It's OK to clear the active flag here without
* grabbing the mutex because nobody else can be scanning the array here,
* and nobody can be attached to this slot and thus access it without
* scanning the array.
*/
LWLockAcquire(ReplicationSlotControlLock, LW_EXCLUSIVE);
slot->active = false;
slot->in_use = false;
LWLockRelease(ReplicationSlotControlLock);
/*
* Slot is dead and doesn't prevent resource removal anymore, recompute
* limits.
*/
ReplicationSlotsComputeRequiredXmin();
ReplicationSlotsComputeRequiredLSN();
/*
* If removing the directory fails, the worst thing that will happen is
* that the user won't be able to create a new slot with the same name
* until the next server restart. We warn about it, but that's all.
*/
if (!rmtree(tmppath, true))
ereport(WARNING,
(errcode_for_file_access(),
errmsg("could not remove directory \"%s\"", tmppath)));
/*
* We release this at the very end, so that nobody starts trying to create
* a slot while we're still cleaning up the detritus of the old one.
*/
LWLockRelease(ReplicationSlotAllocationLock);
}