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pg_failover_slots.c
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pg_failover_slots.c
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/*
* Postgres Failover Slots (pg_failover_slots)
*
* Copyright (c) 2023, EnterpriseDB Corporation.
*/
#include "postgres.h"
#include <dirent.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <unistd.h>
#include "funcapi.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "access/genam.h"
#if PG_VERSION_NUM >= 120000
#include "access/table.h"
#else
#include "access/heapam.h"
#define table_open heap_open
#define table_close heap_close
#endif
#include "access/xact.h"
#if PG_VERSION_NUM >= 150000
#include "access/xlogrecovery.h"
#endif
#include "catalog/indexing.h"
#include "catalog/pg_database.h"
#include "postmaster/bgworker.h"
#if PG_VERSION_NUM >= 130000
#include "postmaster/interrupt.h"
#endif
#include "replication/decode.h"
#include "replication/logical.h"
#include "replication/slot.h"
#include "replication/walreceiver.h"
#include "replication/walsender.h"
#include "storage/ipc.h"
#include "storage/procarray.h"
#include "tcop/tcopprot.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/fmgrprotos.h"
#include "utils/guc.h"
#include "utils/memutils.h"
#include "utils/pg_lsn.h"
#include "utils/resowner.h"
#include "utils/snapmgr.h"
#include "utils/varlena.h"
#include "libpq-fe.h"
#include "libpq/auth.h"
#include "libpq/libpq.h"
#define PG_FAILOVER_SLOTS_VERSION "1.1.0"
PG_MODULE_MAGIC;
#if PG_VERSION_NUM < 130000
#define SignalHandlerForConfigReload PostgresSigHupHandler
#define GetWalRcvFlushRecPtr GetWalRcvWriteRecPtr
#endif
#define EXTENSION_NAME "pg_failover_slots"
#define WORKER_WAIT_FEEDBACK 10000L
typedef struct RemoteSlot
{
char *name;
char *plugin;
char *database;
bool two_phase;
XLogRecPtr restart_lsn;
XLogRecPtr confirmed_lsn;
TransactionId catalog_xmin;
} RemoteSlot;
typedef enum FailoverSlotFilterKey
{
FAILOVERSLOT_FILTER_NAME = 1,
FAILOVERSLOT_FILTER_NAME_LIKE,
FAILOVERSLOT_FILTER_PLUGIN
} FailoverSlotFilterKey;
typedef struct FailoverSlotFilter
{
FailoverSlotFilterKey key;
char *val; /* eg: test_decoding */
} FailoverSlotFilter;
/* Used for physical-before-logical ordering */
static char *standby_slot_names_raw;
static char *standby_slot_names_string = NULL;
List *standby_slot_names = NIL;
int standby_slots_min_confirmed;
XLogRecPtr standby_slot_names_oldest_flush_lsn = InvalidXLogRecPtr;
/* Various configuration */
int worker_nap_time;
char *pg_failover_maintenance_db;
/* Slots to sync */
char *pg_failover_slots_dsn;
char *pg_failover_slot_names;
static char *pg_failover_slot_names_str = NULL;
static List *pg_failover_slot_names_list = NIL;
static bool pg_failover_slots_drop = true;
char *pg_failover_slots_version_str;
void _PG_init(void);
PGDLLEXPORT void pg_failover_slots_main(Datum main_arg);
static bool
check_failover_slot_names(char **newval, void **extra, GucSource source)
{
List *namelist = NIL;
char *rawname = pstrdup(*newval);
bool valid;
valid = SplitIdentifierString(rawname, ',', &namelist);
if (!valid)
GUC_check_errdetail("List syntax is invalid.");
pfree(rawname);
list_free(namelist);
return valid;
}
static void
assign_failover_slot_names(const char *newval, void *extra)
{
MemoryContext old_ctx;
List *slot_names_list = NIL;
ListCell *lc;
/* cleanup memory to prevent leaking or SET/config reload */
if (pg_failover_slot_names_str)
pfree(pg_failover_slot_names_str);
if (pg_failover_slot_names_list)
{
foreach (lc, pg_failover_slot_names_list)
{
FailoverSlotFilter *filter = lfirst(lc);
/* val was pointer to pg_failover_slot_names_str */
pfree(filter);
}
list_free(pg_failover_slot_names_list);
}
pg_failover_slot_names_list = NIL;
/* Allocate memory in long lasting context. */
old_ctx = MemoryContextSwitchTo(TopMemoryContext);
pg_failover_slot_names_str = pstrdup(newval);
SplitIdentifierString(pg_failover_slot_names_str, ',', &slot_names_list);
foreach (lc, slot_names_list)
{
char *raw_val = lfirst(lc);
char *key = strtok(raw_val, ":");
FailoverSlotFilter *filter = palloc(sizeof(FailoverSlotFilter));
filter->val = strtok(NULL, ":");
/* Default key is name */
if (!filter->val)
{
filter->val = key;
filter->key = FAILOVERSLOT_FILTER_NAME;
}
else if (strcmp(key, "name") == 0)
filter->key = FAILOVERSLOT_FILTER_NAME;
else if (strcmp(key, "name_like") == 0)
filter->key = FAILOVERSLOT_FILTER_NAME_LIKE;
else if (strcmp(key, "plugin") == 0)
filter->key = FAILOVERSLOT_FILTER_PLUGIN;
else
ereport(
ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg(
"unrecognized synchronize_failover_slot_names key \"%s\"",
key)));
/* Check that there was just one ':' */
if (strtok(NULL, ":"))
ereport(
ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg(
"unrecognized synchronize_failover_slot_names format")));
pg_failover_slot_names_list =
lappend(pg_failover_slot_names_list, filter);
}
/* Clean the temporary list, but not the contents. */
list_free(slot_names_list);
MemoryContextSwitchTo(old_ctx);
}
static bool
check_standby_slot_names(char **newval, void **extra, GucSource source)
{
List *namelist = NIL;
char *rawname = pstrdup(*newval);
bool valid;
valid = SplitIdentifierString(rawname, ',', &namelist);
if (!valid)
GUC_check_errdetail("List syntax is invalid.");
pfree(rawname);
list_free(namelist);
return valid;
}
static void
assign_standby_slot_names(const char *newval, void *extra)
{
MemoryContext old_ctx;
if (standby_slot_names_string)
pfree(standby_slot_names_string);
if (standby_slot_names)
list_free(standby_slot_names);
/*
* We must invalidate our idea of the oldest lsn in all the named slots if
* we might have changed the list.
*/
standby_slot_names_oldest_flush_lsn = InvalidXLogRecPtr;
old_ctx = MemoryContextSwitchTo(TopMemoryContext);
standby_slot_names_string = pstrdup(newval);
(void) SplitIdentifierString(standby_slot_names_string, ',',
&standby_slot_names);
(void) MemoryContextSwitchTo(old_ctx);
}
/*
* Get failover slots from upstream
*/
static List *
remote_get_primary_slot_info(PGconn *conn, List *slot_filter)
{
PGresult *res;
int i;
char *op = "";
List *slots = NIL;
ListCell *lc;
StringInfoData query;
initStringInfo(&query);
if (PQserverVersion(conn) >= 140000)
{
appendStringInfoString(
&query,
"SELECT slot_name, plugin, database, two_phase, catalog_xmin, restart_lsn, confirmed_flush_lsn"
" FROM pg_catalog.pg_replication_slots"
" WHERE database IS NOT NULL AND (");
}
else
{
appendStringInfoString(
&query,
"SELECT slot_name, plugin, database, false AS two_phase, catalog_xmin, restart_lsn, confirmed_flush_lsn"
" FROM pg_catalog.pg_replication_slots"
" WHERE database IS NOT NULL AND (");
}
foreach (lc, slot_filter)
{
FailoverSlotFilter *filter = lfirst(lc);
switch (filter->key)
{
case FAILOVERSLOT_FILTER_NAME:
appendStringInfo(
&query, " %s slot_name OPERATOR(pg_catalog.=) %s", op,
PQescapeLiteral(conn, filter->val, strlen(filter->val)));
break;
case FAILOVERSLOT_FILTER_NAME_LIKE:
appendStringInfo(
&query, " %s slot_name LIKE %s", op,
PQescapeLiteral(conn, filter->val, strlen(filter->val)));
break;
case FAILOVERSLOT_FILTER_PLUGIN:
appendStringInfo(
&query, " %s plugin OPERATOR(pg_catalog.=) %s", op,
PQescapeLiteral(conn, filter->val, strlen(filter->val)));
break;
default:
Assert(0);
elog(ERROR, "unrecognized slot filter key %u", filter->key);
}
op = "OR";
}
appendStringInfoString(&query, ")");
res = PQexec(conn, query.data);
pfree(query.data);
if (PQresultStatus(res) != PGRES_TUPLES_OK)
elog(ERROR, "could not fetch slot information from provider: %s\n",
res != NULL ? PQresultErrorMessage(res) : PQerrorMessage(conn));
for (i = 0; i < PQntuples(res); i++)
{
RemoteSlot *slot = palloc0(sizeof(RemoteSlot));
slot->name = pstrdup(PQgetvalue(res, i, 0));
slot->plugin = pstrdup(PQgetvalue(res, i, 1));
slot->database = pstrdup(PQgetvalue(res, i, 2));
parse_bool(PQgetvalue(res, i, 3), &slot->two_phase);
slot->catalog_xmin = !PQgetisnull(res, i, 4) ?
atoi(PQgetvalue(res, i, 4)) :
InvalidTransactionId;
slot->restart_lsn =
!PQgetisnull(res, i, 5) ?
DatumGetLSN(DirectFunctionCall1(
pg_lsn_in, CStringGetDatum(PQgetvalue(res, i, 5)))) :
InvalidXLogRecPtr;
slot->confirmed_lsn =
!PQgetisnull(res, i, 6) ?
DatumGetLSN(DirectFunctionCall1(
pg_lsn_in, CStringGetDatum(PQgetvalue(res, i, 6)))) :
InvalidXLogRecPtr;
slots = lappend(slots, slot);
}
PQclear(res);
return slots;
}
static XLogRecPtr
remote_get_physical_slot_lsn(PGconn *conn, const char *slot_name)
{
PGresult *res;
XLogRecPtr lsn;
StringInfoData query;
initStringInfo(&query);
appendStringInfo(&query,
"SELECT restart_lsn"
" FROM pg_catalog.pg_replication_slots"
" WHERE slot_name OPERATOR(pg_catalog.=) %s",
PQescapeLiteral(conn, slot_name, strlen(slot_name)));
res = PQexec(conn, query.data);
if (PQresultStatus(res) != PGRES_TUPLES_OK)
elog(ERROR, "could not fetch slot information from provider: %s\n",
res != NULL ? PQresultErrorMessage(res) : PQerrorMessage(conn));
if (PQntuples(res) != 1)
elog(ERROR, "physical slot %s not found on primary", slot_name);
if (PQgetisnull(res, 0, 0))
lsn = InvalidXLogRecPtr;
else
lsn = DatumGetLSN(DirectFunctionCall1(
pg_lsn_in, CStringGetDatum(PQgetvalue(res, 0, 0))));
PQclear(res);
return lsn;
}
/*
* Can't use get_database_oid from dbcommands.c because it does not work
* without db connection.
*/
static Oid
get_database_oid(const char *dbname)
{
HeapTuple tuple;
Relation relation;
SysScanDesc scan;
ScanKeyData key[1];
Oid dboid = InvalidOid;
/*
* form a scan key
*/
ScanKeyInit(&key[0], Anum_pg_database_datname, BTEqualStrategyNumber,
F_NAMEEQ, CStringGetDatum(dbname));
/*
* Open pg_database and fetch a tuple. Force heap scan if we haven't yet
* built the critical shared relcache entries (i.e., we're starting up
* without a shared relcache cache file).
*/
relation = table_open(DatabaseRelationId, AccessShareLock);
scan = systable_beginscan(relation, DatabaseNameIndexId,
criticalSharedRelcachesBuilt, NULL, 1, key);
tuple = systable_getnext(scan);
/* Must copy tuple before releasing buffer */
if (HeapTupleIsValid(tuple))
#if PG_VERSION_NUM < 120000
dboid = HeapTupleGetOid(tuple);
#else
{
Form_pg_database datForm = (Form_pg_database) GETSTRUCT(tuple);
dboid = datForm->oid;
}
#endif
else
ereport(ERROR, (errcode(ERRCODE_UNDEFINED_DATABASE),
errmsg("database \"%s\" does not exist", dbname)));
/* all done */
systable_endscan(scan);
table_close(relation, AccessShareLock);
return dboid;
}
/*
* Fill connection string info based on config.
*
* This is slightly complicated because we default to primary_conninfo if
* user didn't explicitly set anything and we might need to request explicit
* database name override, that's why we need dedicated function for this.
*/
static void
make_sync_failover_slots_dsn(StringInfo connstr, char *db_name)
{
Assert(db_name);
if (pg_failover_slots_dsn && strlen(pg_failover_slots_dsn) > 0)
{
if (db_name)
appendStringInfo(connstr, "%s dbname=%s", pg_failover_slots_dsn,
db_name);
else
appendStringInfoString(connstr, pg_failover_slots_dsn);
}
else
{
Assert(WalRcv);
appendStringInfo(connstr, "%s dbname=%s", WalRcv->conninfo, db_name);
}
}
/*
* Connect to remote pg server
*/
static PGconn *
remote_connect(const char *connstr, const char *appname)
{
#define CONN_PARAM_ARRAY_SIZE 8
int i = 0;
PGconn *conn;
const char *keys[CONN_PARAM_ARRAY_SIZE];
const char *vals[CONN_PARAM_ARRAY_SIZE];
StringInfoData s;
initStringInfo(&s);
appendStringInfoString(&s, connstr);
keys[i] = "dbname";
vals[i] = connstr;
i++;
keys[i] = "application_name";
vals[i] = appname;
i++;
keys[i] = "connect_timeout";
vals[i] = "30";
i++;
keys[i] = "keepalives";
vals[i] = "1";
i++;
keys[i] = "keepalives_idle";
vals[i] = "20";
i++;
keys[i] = "keepalives_interval";
vals[i] = "20";
i++;
keys[i] = "keepalives_count";
vals[i] = "5";
i++;
keys[i] = NULL;
vals[i] = NULL;
Assert(i <= CONN_PARAM_ARRAY_SIZE);
/*
* We use the expand_dbname parameter to process the connection string
* (or URI), and pass some extra options.
*/
conn = PQconnectdbParams(keys, vals, /* expand_dbname = */ true);
if (PQstatus(conn) != CONNECTION_OK)
{
ereport(ERROR,
(errmsg("could not connect to the postgresql server: %s",
PQerrorMessage(conn)),
errdetail("dsn was: %s", s.data)));
}
resetStringInfo(&s);
elog(DEBUG2, "established connection to remote backend with pid %d",
PQbackendPID(conn));
return conn;
}
/*
* Wait for remote slot to pass locally reserved position.
*
* Wait until the slot named in 'remote_slot' on the host at 'conn' has all its
* requirements satisfied by the local slot 'slot' by polling 'conn'. This
* relies on us having already reserved the WAL for the old position of
* `remote_slot` so `slot` can't continue to advance.
*/
static bool
wait_for_primary_slot_catchup(ReplicationSlot *slot, RemoteSlot *remote_slot)
{
List *slots;
PGconn *conn;
StringInfoData connstr;
TimestampTz cb_wait_start =
0; /* first invocation should happen immediately */
elog(
LOG,
"waiting for remote slot %s lsn (%X/%X) and catalog xmin (%u) to pass local slot lsn (%X/%X) and catalog xmin (%u)",
remote_slot->name, (uint32) (remote_slot->restart_lsn >> 32),
(uint32) (remote_slot->restart_lsn), remote_slot->catalog_xmin,
(uint32) (slot->data.restart_lsn >> 32),
(uint32) (slot->data.restart_lsn), slot->data.catalog_xmin);
initStringInfo(&connstr);
/*
* Append the dbname of the remote slot. We don't use a generic db
* like postgres here because plugin callback bellow might want to invoke
* extension functions.
*/
make_sync_failover_slots_dsn(&connstr, remote_slot->database);
conn = remote_connect(connstr.data, "pg_failover_slots");
pfree(connstr.data);
for (;;)
{
RemoteSlot *new_slot;
int rc;
FailoverSlotFilter *filter = palloc(sizeof(FailoverSlotFilter));
XLogRecPtr receivePtr;
CHECK_FOR_INTERRUPTS();
if (!RecoveryInProgress())
{
/*
* The remote slot didn't pass the locally reserved position
* at the time of local promotion, so it's not safe to use.
*/
ereport(
WARNING,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg(
"replication slot sync wait for slot %s interrupted by promotion",
remote_slot->name)));
PQfinish(conn);
return false;
}
filter->key = FAILOVERSLOT_FILTER_NAME;
filter->val = remote_slot->name;
slots = remote_get_primary_slot_info(conn, list_make1(filter));
if (!list_length(slots))
{
/* Slot on provider vanished */
PQfinish(conn);
return false;
}
receivePtr = GetWalRcvFlushRecPtr(NULL, NULL);
Assert(list_length(slots) == 1);
new_slot = linitial(slots);
if (new_slot->restart_lsn > receivePtr)
new_slot->restart_lsn = receivePtr;
if (new_slot->confirmed_lsn > receivePtr)
new_slot->confirmed_lsn = receivePtr;
if (new_slot->restart_lsn >= slot->data.restart_lsn &&
TransactionIdFollowsOrEquals(new_slot->catalog_xmin,
MyReplicationSlot->data.catalog_xmin))
{
remote_slot->restart_lsn = new_slot->restart_lsn;
remote_slot->confirmed_lsn = new_slot->confirmed_lsn;
remote_slot->catalog_xmin = new_slot->catalog_xmin;
PQfinish(conn);
return true;
}
/*
* Invoke any callbacks that will help move the slots along
*/
if (TimestampDifferenceExceeds(
cb_wait_start, GetCurrentTimestamp(),
Min(wal_retrieve_retry_interval * 5, PG_WAIT_EXTENSION)))
{
if (cb_wait_start > 0)
elog(
LOG,
"still waiting for remote slot %s lsn (%X/%X) and catalog xmin (%u) to pass local slot lsn (%X/%X) and catalog xmin (%u)",
remote_slot->name, (uint32) (new_slot->restart_lsn >> 32),
(uint32) (new_slot->restart_lsn), new_slot->catalog_xmin,
(uint32) (slot->data.restart_lsn >> 32),
(uint32) (slot->data.restart_lsn),
slot->data.catalog_xmin);
cb_wait_start = GetCurrentTimestamp();
}
rc =
WaitLatch(MyLatch, WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
wal_retrieve_retry_interval, PG_WAIT_EXTENSION);
if (rc & WL_POSTMASTER_DEATH)
proc_exit(1);
ResetLatch(MyLatch);
}
}
/*
* Synchronize one logical replication slot's state from the master to this
* standby, creating it if necessary.
*
* Note that this only works safely because we know for sure that this is
* executed on standby where primary has another slot which reserves resources
* at the position to which we are moving the local slot to.
*
* This standby uses a physical replication slot to connect to the master so it
* can send the xmin and catalog_xmin separately over hot_standby_feedback. Our
* physical slot on the master ensures the master's catalog_xmin never goes
* below ours after the initial setup period.
*/
static void
synchronize_one_slot(RemoteSlot *remote_slot)
{
int i;
bool found = false;
if (!RecoveryInProgress())
{
/* Should only happen when promotion occurs at the same time we sync */
ereport(
WARNING,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg(
"attempted to sync slot from master when not in recovery")));
return;
}
SetCurrentStatementStartTimestamp();
StartTransactionCommand();
PushActiveSnapshot(GetTransactionSnapshot());
/* Search for the named slot locally */
LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
for (i = 0; i < max_replication_slots; i++)
{
ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
/* Not in use, not interesting. */
if (!s->in_use)
continue;
if (strcmp(NameStr(s->data.name), remote_slot->name) == 0)
{
found = true;
break;
}
}
LWLockRelease(ReplicationSlotControlLock);
/*
* Remote slot exists locally, acquire and move. There's a race here where
* the slot could've been dropped since we checked, but we'll just ERROR
* out in `ReplicationSlotAcquire` and retry next loop so it's harmless.
*
* Moving the slot this way does not do logical decoding. We're not
* processing WAL, we're just updating the slot metadata.
*/
if (found)
{
ReplicationSlotAcquire(remote_slot->name, true);
/*
* We can't satisfy this remote slot's requirements with our known-safe
* local restart_lsn, catalog_xmin and xmin.
*
* This shouldn't happen for existing slots unless someone else messed
* with our physical replication slot on the master.
*/
if (remote_slot->restart_lsn < MyReplicationSlot->data.restart_lsn ||
TransactionIdPrecedes(remote_slot->catalog_xmin,
MyReplicationSlot->data.catalog_xmin))
{
elog(
WARNING,
"not synchronizing slot %s; synchronization would move it backward",
remote_slot->name);
ReplicationSlotRelease();
PopActiveSnapshot();
CommitTransactionCommand();
return;
}
LogicalConfirmReceivedLocation(remote_slot->confirmed_lsn);
LogicalIncreaseXminForSlot(remote_slot->confirmed_lsn,
remote_slot->catalog_xmin);
LogicalIncreaseRestartDecodingForSlot(remote_slot->confirmed_lsn,
remote_slot->restart_lsn);
ReplicationSlotMarkDirty();
ReplicationSlotSave();
elog(
DEBUG2,
"synchronized existing slot %s to lsn (%X/%X) and catalog xmin (%u)",
remote_slot->name, (uint32) (remote_slot->restart_lsn >> 32),
(uint32) (remote_slot->restart_lsn), remote_slot->catalog_xmin);
}
/*
* Otherwise create the local slot and initialize it to the state of the
* upstream slot. There's a race here where the slot could've been
* concurrently created, but we'll just ERROR out and retry so it's
* harmless.
*/
else
{
TransactionId xmin_horizon = InvalidTransactionId;
ReplicationSlot *slot;
/*
* We have to create the slot to reserve its name and resources, but
* don't want it to persist if we fail.
*/
#if PG_VERSION_NUM >= 170000
ReplicationSlotCreate(remote_slot->name, true, RS_EPHEMERAL,
remote_slot->two_phase, false, false);
#elif PG_VERSION_NUM >= 140000
ReplicationSlotCreate(remote_slot->name, true, RS_EPHEMERAL,
remote_slot->two_phase);
#else
ReplicationSlotCreate(remote_slot->name, true, RS_EPHEMERAL);
#endif
slot = MyReplicationSlot;
SpinLockAcquire(&slot->mutex);
slot->data.database = get_database_oid(remote_slot->database);
strlcpy(NameStr(slot->data.plugin), remote_slot->plugin, NAMEDATALEN);
SpinLockRelease(&slot->mutex);
/*
* Stop our physical slot from advancing past the position needed
* by the new remote slot by making its reservations locally
* effective. It's OK if we can't guarantee their safety yet,
* the slot isn't visible to anyone else at this point.
*/
ReplicationSlotReserveWal();
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
xmin_horizon = GetOldestSafeDecodingTransactionId(true);
slot->effective_catalog_xmin = xmin_horizon;
slot->data.catalog_xmin = xmin_horizon;
ReplicationSlotsComputeRequiredXmin(true);
LWLockRelease(ProcArrayLock);
/*
* Our xmin and/or catalog_xmin may be > that required by one or more
* of the slots we are trying to sync from the master, and/or we don't
* have enough retained WAL for the slot's restart_lsn.
*
* If we persist the slot locally in that state it'll make a false
* promise we can't satisfy.
*
* This can happen if this replica is fairly new or has only recently
* started failover slot sync.
*
* TODO: Don't stop synchronization of other slots for this, we can't
* add timeout because that could result in some slots never being
* synchronized as they will always be behind the physical slot.
*/
if (remote_slot->restart_lsn < MyReplicationSlot->data.restart_lsn ||
TransactionIdPrecedes(remote_slot->catalog_xmin,
MyReplicationSlot->data.catalog_xmin))
{
if (!wait_for_primary_slot_catchup(MyReplicationSlot, remote_slot))
{
/* Provider slot didn't catch up to locally reserved position
*/
ReplicationSlotRelease();
PopActiveSnapshot();
CommitTransactionCommand();
return;
}
}
/*
* We can locally satisfy requirements of remote slot's current
* position now. Apply the new position if any and make it persistent.
*/
LogicalConfirmReceivedLocation(remote_slot->confirmed_lsn);
LogicalIncreaseXminForSlot(remote_slot->confirmed_lsn,
remote_slot->catalog_xmin);
LogicalIncreaseRestartDecodingForSlot(remote_slot->confirmed_lsn,
remote_slot->restart_lsn);
ReplicationSlotMarkDirty();
ReplicationSlotPersist();
elog(DEBUG1,
"synchronized new slot %s to lsn (%X/%X) and catalog xmin (%u)",
remote_slot->name, (uint32) (remote_slot->restart_lsn >> 32),
(uint32) (remote_slot->restart_lsn), remote_slot->catalog_xmin);
}
ReplicationSlotRelease();
PopActiveSnapshot();
CommitTransactionCommand();
}
/*
* Synchronize the slot states from master to standby.
*
* This logic emulates the "failover slots" behaviour unsuccessfully proposed
* for 9.6 using the PostgreSQL 10 features "catalog xmin in hot standby
* feedback" and "logical decoding follows timeline switches".
*
* This is only called in recovery from main loop of manager and only in PG10+
* because in older versions the manager worker uses
* bgw_start_time = BgWorkerStart_RecoveryFinished.
*
* We could technically synchronize slot positions even on older versions of
* PostgreSQL but since logical decoding can't go over the timeline switch
* before PG10, it's pointless to have slots synchronized. Also, older versions
* can't keep catalog_xmin separate from xmin in hot standby feedback, so
* sending the feedback we need to preserve our catalog_xmin could cause severe
* table bloat on the master.
*
* This runs periodically. That's safe when the slots on the master already
* exist locally because we have their resources reserved via hot standby
* feedback. New subscriptions can't move that position backwards... but we
* won't immediately know they exist when the master creates them. So there's a
* window after each new subscription is created on the master where failover
* to this standby will break that subscription.
*/
static long
synchronize_failover_slots(long sleep_time)
{
List *slots;
ListCell *lc;
PGconn *conn;
XLogRecPtr safe_lsn;
XLogRecPtr lsn = InvalidXLogRecPtr;
static bool was_lsn_safe = false;
bool is_lsn_safe = false;
StringInfoData connstr;
if (!WalRcv || !HotStandbyActive() ||
list_length(pg_failover_slot_names_list) == 0)
return sleep_time;
/* XXX should these be errors or just soft return like above? */
if (!hot_standby_feedback)
elog(
ERROR,
"cannot synchronize replication slot positions because hot_standby_feedback is off");
if (WalRcv->slotname[0] == '\0')
elog(
ERROR,
"cannot synchronize replication slot positions because primary_slot_name is not set");
elog(DEBUG1, "starting replication slot synchronization from primary");
initStringInfo(&connstr);
make_sync_failover_slots_dsn(&connstr, pg_failover_maintenance_db);
conn = remote_connect(connstr.data, "pg_failover_slots");
/*
* Do not synchronize WAL decoder slots on a physical standy.
*
* WAL decoder slots are used to produce LCRs. These LCRs are not
* synchronized on a physical standby after initial backup and hence are
* not included in the base backup. Thus WAL decoder slots, if synchronized
* on physical standby, do not reflect the status of LCR directory as they
* do on primary.
*
* There are other slots whose WAL senders use LCRs. These other slots are
* synchronized and used after promotion. Since the WAL decoder slots are
* ahead of these other slots, the WAL decoder when started after promotion
* might miss LCRs required by WAL senders of the other slots. This would
* cause data inconsistency after promotion.
*
* Hence do not synchronize WAL decoder slot. Those will be created after
* promotion
*/
slots = remote_get_primary_slot_info(conn, pg_failover_slot_names_list);
safe_lsn = remote_get_physical_slot_lsn(conn, WalRcv->slotname);
/*
* Delete locally-existing slots that don't exist on the master.
*/
for (;;)
{
int i;
char *dropslot = NULL;
LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
for (i = 0; i < max_replication_slots; i++)
{
ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
bool active;
bool found = false;
active = (s->active_pid != 0);
/* Only check inactive slots. */
if (!s->in_use || active)
continue;
/* Only check for logical slots. */
if (SlotIsPhysical(s))
continue;
/* Try to find slot in slots returned by primary. */
foreach (lc, slots)
{
RemoteSlot *remote_slot = lfirst(lc);
if (strcmp(NameStr(s->data.name), remote_slot->name) == 0)
{
found = true;
break;
}
}
/*
* Not found, should be dropped if synchronize_failover_slots_drop
* is enabled.
*/
if (!found && pg_failover_slots_drop)
{
dropslot = pstrdup(NameStr(s->data.name));
break;
}
}
LWLockRelease(ReplicationSlotControlLock);
if (dropslot)
{
elog(WARNING, "dropping replication slot \"%s\"", dropslot);
ReplicationSlotDrop(dropslot, false);
pfree(dropslot);
}
else
break;
}
if (!list_length(slots))
{
PQfinish(conn);
return sleep_time;
}
/* Find oldest restart_lsn still needed by any failover slot. */
foreach (lc, slots)
{
RemoteSlot *remote_slot = lfirst(lc);