Anna Akenteva писал 2020-04-08 22:36:
On 2020-04-08 04:09, Kyotaro Horiguchi wrote:
I like your suggested keywords! I think that "AFTER" + "WITHIN" sound
the most natural. We could completely give up the LSN keyword for now.
The final command could look something like:
BEGIN AFTER ‘0/303EC60’ WITHIN '5 seconds';
or
BEGIN AFTER ‘0/303EC60’ WITHIN 5000;
Hello,
I've changed the syntax of the command from BEGIN [ WAIT FOR LSN value [
TIMEOUT delay ]] to BEGIN [ AFTER value [ WITHIN delay ]] and removed
all the unnecessary keywords.
Best regards,
Alexandra Pervushina.
diff --git a/doc/src/sgml/ref/begin.sgml b/doc/src/sgml/ref/begin.sgml
index 53eac922645..c5bf1a99039 100644
--- a/doc/src/sgml/ref/begin.sgml
+++ b/doc/src/sgml/ref/begin.sgml
@@ -21,7 +21,7 @@ doc/src/sgml/ref/begin.sgml
<refsynopsisdiv>
<synopsis>
-BEGIN [ WORK | TRANSACTION ] [ <replaceable class="parameter">transaction_mode</replaceable> [, ...] ]
+BEGIN [ WORK | TRANSACTION ] [ <replaceable class="parameter">transaction_mode</replaceable> [, ...] ] [AFTER <replaceable class="parameter">lsn_value</replaceable> [WITHIN <replaceable class="parameter">number_of_milliseconds</replaceable> ] ]
<phrase>where <replaceable class="parameter">transaction_mode</replaceable> is one of:</phrase>
@@ -63,6 +63,17 @@ BEGIN [ WORK | TRANSACTION ] [ <replaceable class="parameter">transaction_mode</
<xref linkend="sql-set-transaction"/>
was executed.
</para>
+
+ <para>
+ The <literal>BEGIN AFTER</literal> clause allows to wait for the target log
+ sequence number (<acronym>LSN</acronym>) to be replayed on standby before
+ starting the transaction in <productname>PostgreSQL</productname> databases
+ with primary-standby asynchronous replication. Wait time can be limited by
+ specifying a timeout, which is measured in milliseconds and must be a positive
+ integer. If <acronym>LSN</acronym> was not reached before timeout, transaction
+ doesn't begin. Waiting can be interrupted using <literal>Ctrl+C</literal>, or
+ by shutting down the <literal>postgres</literal> server.
+ </para>
</refsect1>
<refsect1>
@@ -146,6 +157,10 @@ BEGIN;
different purpose in embedded SQL. You are advised to be careful
about the transaction semantics when porting database applications.
</para>
+
+ <para>
+ There is no <command>AFTER</command> clause in the SQL standard.
+ </para>
</refsect1>
<refsect1>
diff --git a/doc/src/sgml/ref/start_transaction.sgml b/doc/src/sgml/ref/start_transaction.sgml
index d5dfa413aeb..ea9b0b43fd0 100644
--- a/doc/src/sgml/ref/start_transaction.sgml
+++ b/doc/src/sgml/ref/start_transaction.sgml
@@ -21,7 +21,7 @@ doc/src/sgml/ref/start_transaction.sgml
<refsynopsisdiv>
<synopsis>
-START TRANSACTION [ <replaceable class="parameter">transaction_mode</replaceable> [, ...] ]
+START TRANSACTION [ <replaceable class="parameter">transaction_mode</replaceable> [, ...] ] [ AFTER <replaceable class="parameter">lsn_value</replaceable> [WITHIN <replaceable class="parameter">number_of_milliseconds</replaceable> ] ]
<phrase>where <replaceable class="parameter">transaction_mode</replaceable> is one of:</phrase>
@@ -40,6 +40,17 @@ START TRANSACTION [ <replaceable class="parameter">transaction_mode</replaceable
characteristics, as if <xref linkend="sql-set-transaction"/> was executed. This is the same
as the <xref linkend="sql-begin"/> command.
</para>
+
+ <para>
+ The <literal>WAIT FOR</literal> clause allows to wait for the target log
+ sequence number (<acronym>LSN</acronym>) to be replayed on standby before
+ starting the transaction in <productname>PostgreSQL</productname> databases
+ with primary-standby asynchronous replication. Wait time can be limited by
+ specifying a timeout, which is measured in milliseconds and must be a positive
+ integer. If <acronym>LSN</acronym> was not reached before timeout, transaction
+ doesn't begin. Waiting can be interrupted using <literal>Ctrl+C</literal>, or
+ by shutting down the <literal>postgres</literal> server.
+ </para>
</refsect1>
<refsect1>
@@ -78,6 +89,10 @@ START TRANSACTION [ <replaceable class="parameter">transaction_mode</replaceable
omitted.
</para>
+ <para>
+ There is no <command>WAIT FOR</command> clause in the SQL standard.
+ </para>
+
<para>
See also the compatibility section of <xref linkend="sql-set-transaction"/>.
</para>
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 9d3f1c12fc5..27e964c8111 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -42,6 +42,7 @@
#include "catalog/pg_database.h"
#include "commands/progress.h"
#include "commands/tablespace.h"
+#include "commands/wait.h"
#include "common/controldata_utils.h"
#include "executor/instrument.h"
#include "miscadmin.h"
@@ -7387,6 +7388,15 @@ StartupXLOG(void)
break;
}
+ /*
+ * If we replayed an LSN that someone was waiting for,
+ * set latches in shared memory array to notify the waiter.
+ */
+ if (XLogCtl->lastReplayedEndRecPtr >= GetMinWaitedLSN())
+ {
+ WaitSetLatch(XLogCtl->lastReplayedEndRecPtr);
+ }
+
/* Else, try to fetch the next WAL record */
record = ReadRecord(xlogreader, LOG, false);
} while (record != NULL);
diff --git a/src/backend/commands/Makefile b/src/backend/commands/Makefile
index d4815d3ce65..9b310926c12 100644
--- a/src/backend/commands/Makefile
+++ b/src/backend/commands/Makefile
@@ -57,6 +57,7 @@ OBJS = \
user.o \
vacuum.o \
variable.o \
- view.o
+ view.o \
+ wait.o
include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/commands/wait.c b/src/backend/commands/wait.c
new file mode 100644
index 00000000000..84195e2a7df
--- /dev/null
+++ b/src/backend/commands/wait.c
@@ -0,0 +1,282 @@
+/*-------------------------------------------------------------------------
+ *
+ * wait.c
+ * Implements BEGIN AFTER, which allows waiting for events such as
+ * LSN having been replayed on replica.
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 2020, Regents of PostgresPro
+ *
+ * IDENTIFICATION
+ * src/backend/commands/wait.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <math.h>
+
+#include "access/xlog.h"
+#include "access/xlogdefs.h"
+#include "commands/wait.h"
+#include "funcapi.h"
+#include "miscadmin.h"
+#include "pgstat.h"
+#include "storage/backendid.h"
+#include "storage/pmsignal.h"
+#include "storage/proc.h"
+#include "storage/shmem.h"
+#include "storage/sinvaladt.h"
+#include "storage/spin.h"
+#include "utils/builtins.h"
+#include "utils/pg_lsn.h"
+#include "utils/timestamp.h"
+
+/* Add to shared memory array */
+static void AddWaitedLSN(XLogRecPtr lsn_to_wait);
+
+/* Shared memory structure */
+typedef struct
+{
+ int backend_maxid;
+ pg_atomic_uint64 min_lsn; /* XLogRecPtr of minimal waited for LSN */
+ slock_t mutex;
+ /* LSNs that different backends are waiting */
+ XLogRecPtr lsn[FLEXIBLE_ARRAY_MEMBER];
+} WaitState;
+
+static WaitState *state;
+
+/*
+ * Add the wait event of the current backend to shared memory array
+ */
+static void
+AddWaitedLSN(XLogRecPtr lsn_to_wait)
+{
+ SpinLockAcquire(&state->mutex);
+ if (state->backend_maxid < MyBackendId)
+ state->backend_maxid = MyBackendId;
+
+ state->lsn[MyBackendId] = lsn_to_wait;
+
+ if (lsn_to_wait < state->min_lsn.value)
+ state->min_lsn.value = lsn_to_wait;
+ SpinLockRelease(&state->mutex);
+}
+
+/*
+ * Delete wait event of the current backend from the shared memory array.
+ */
+void
+DeleteWaitedLSN(void)
+{
+ int i;
+ XLogRecPtr lsn_to_delete;
+
+ SpinLockAcquire(&state->mutex);
+
+ lsn_to_delete = state->lsn[MyBackendId];
+ state->lsn[MyBackendId] = InvalidXLogRecPtr;
+
+ /* If we are deleting the minimal LSN, then choose the next min_lsn */
+ if (lsn_to_delete != InvalidXLogRecPtr &&
+ lsn_to_delete == state->min_lsn.value)
+ {
+ state->min_lsn.value = PG_UINT64_MAX;
+ for (i = 2; i <= state->backend_maxid; i++)
+ if (state->lsn[i] != InvalidXLogRecPtr &&
+ state->lsn[i] < state->min_lsn.value)
+ state->min_lsn.value = state->lsn[i];
+ }
+
+ /* If deleting from the end of the array, shorten the array's used part */
+ if (state->backend_maxid == MyBackendId)
+ for (i = (MyBackendId); i >= 2; i--)
+ if (state->lsn[i] != InvalidXLogRecPtr)
+ {
+ state->backend_maxid = i;
+ break;
+ }
+
+ SpinLockRelease(&state->mutex);
+}
+
+/*
+ * Report amount of shared memory space needed for WaitState
+ */
+Size
+WaitShmemSize(void)
+{
+ Size size;
+
+ size = offsetof(WaitState, lsn);
+ size = add_size(size, mul_size(MaxBackends + 1, sizeof(XLogRecPtr)));
+ return size;
+}
+
+/*
+ * Initialize an array of events to wait for in shared memory
+ */
+void
+WaitShmemInit(void)
+{
+ bool found;
+ uint32 i;
+
+ state = (WaitState *) ShmemInitStruct("pg_wait_lsn",
+ WaitShmemSize(),
+ &found);
+ if (!found)
+ {
+ SpinLockInit(&state->mutex);
+
+ for (i = 0; i < (MaxBackends + 1); i++)
+ state->lsn[i] = InvalidXLogRecPtr;
+
+ state->backend_maxid = 0;
+ state->min_lsn.value = PG_UINT64_MAX;
+ }
+}
+
+/*
+ * Set latches in shared memory to signal that new LSN has been replayed
+ */
+void
+WaitSetLatch(XLogRecPtr cur_lsn)
+{
+ uint32 i;
+ int backend_maxid;
+ PGPROC *backend;
+
+ SpinLockAcquire(&state->mutex);
+ backend_maxid = state->backend_maxid;
+
+ for (i = 2; i <= backend_maxid; i++)
+ {
+ backend = BackendIdGetProc(i);
+
+ if (backend && state->lsn[i] != 0 &&
+ state->lsn[i] <= cur_lsn)
+ {
+ SetLatch(&backend->procLatch);
+ }
+ }
+ SpinLockRelease(&state->mutex);
+}
+
+/*
+ * Get minimal LSN that someone waits for
+ */
+XLogRecPtr
+GetMinWaitedLSN(void)
+{
+ return state->min_lsn.value;
+}
+
+/*
+ * On WAIT use a latch to wait till LSN is replayed,
+ * postmaster dies or timeout happens. Timeout is specified in milliseconds.
+ * Returns true if LSN was reached and false otherwise.
+ */
+bool
+WaitUtility(XLogRecPtr target_lsn, const int timeout_ms)
+{
+ XLogRecPtr cur_lsn = GetXLogReplayRecPtr(NULL);
+ int latch_events;
+ float8 endtime;
+ bool res = false;
+ bool wait_forever = (timeout_ms <= 0);
+
+ endtime = GetNowFloat() + timeout_ms / 1000.0;
+
+ latch_events = WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH;
+
+ /* Check if we already reached the needed LSN */
+ if (cur_lsn >= target_lsn)
+ return true;
+
+ AddWaitedLSN(target_lsn);
+
+ for (;;)
+ {
+ int rc;
+ float8 time_left = 0;
+ long time_left_ms = 0;
+
+ time_left = endtime - GetNowFloat();
+
+ /* Use 100 ms as the default timeout to check for interrupts */
+ if (wait_forever || time_left < 0 || time_left > 0.1)
+ time_left_ms = 100;
+ else
+ time_left_ms = (long) ceil(time_left * 1000.0);
+
+ /* If interrupt, LockErrorCleanup() will do DeleteWaitedLSN() for us */
+ CHECK_FOR_INTERRUPTS();
+
+ /* If postmaster dies, finish immediately */
+ if (!PostmasterIsAlive())
+ break;
+
+ rc = WaitLatch(MyLatch, latch_events, time_left_ms,
+ WAIT_EVENT_CLIENT_READ);
+
+ ResetLatch(MyLatch);
+
+ if (rc & WL_LATCH_SET)
+ cur_lsn = GetXLogReplayRecPtr(NULL);
+
+ if (rc & WL_TIMEOUT)
+ {
+ cur_lsn = GetXLogReplayRecPtr(NULL);
+ /* If the time specified by user has passed, stop waiting */
+ time_left = endtime - GetNowFloat();
+ if (!wait_forever && time_left <= 0.0)
+ break;
+ }
+
+ /* If LSN has been replayed */
+ if (target_lsn <= cur_lsn)
+ break;
+ }
+
+ DeleteWaitedLSN();
+
+ if (cur_lsn < target_lsn)
+ ereport(WARNING,
+ (errcode(ERRCODE_NO_ACTIVE_SQL_TRANSACTION),
+ errmsg("didn't start transaction because LSN was not reached"),
+ errhint("Try to increase wait time.")));
+ else
+ res = true;
+
+ return res;
+}
+
+/*
+ * Implementation of BEGIN AFTER
+ */
+int
+WaitMain(WaitClause *stmt, DestReceiver *dest)
+{
+ TupleDesc tupdesc;
+ TupOutputState *tstate;
+ XLogRecPtr target_lsn;
+ bool res = false;
+
+ target_lsn = DatumGetLSN(DirectFunctionCall1(pg_lsn_in,
+ CStringGetDatum(stmt->lsn)));
+ res = WaitUtility(target_lsn, stmt->timeout);
+
+ /* Need a tuple descriptor representing a single TEXT column */
+ tupdesc = CreateTemplateTupleDesc(1);
+ TupleDescInitEntry(tupdesc, (AttrNumber) 1, "LSN reached", TEXTOID, -1, 0);
+
+ /* Prepare for projection of tuples */
+ tstate = begin_tup_output_tupdesc(dest, tupdesc, &TTSOpsMinimalTuple);
+
+ /* Send the result */
+ do_text_output_oneline(tstate, res ? "t" : "f");
+ end_tup_output(tstate);
+ return res;
+}
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index d8cf87e6d08..df2a68156cc 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -3749,10 +3749,22 @@ _copyTransactionStmt(const TransactionStmt *from)
COPY_STRING_FIELD(savepoint_name);
COPY_STRING_FIELD(gid);
COPY_SCALAR_FIELD(chain);
+ COPY_NODE_FIELD(wait);
return newnode;
}
+static WaitClause *
+_copyWaitClause(const WaitClause *from)
+{
+ WaitClause *newnode = makeNode(WaitClause);
+
+ COPY_STRING_FIELD(lsn);
+ COPY_SCALAR_FIELD(timeout);
+
+ return newnode;
+};
+
static CompositeTypeStmt *
_copyCompositeTypeStmt(const CompositeTypeStmt *from)
{
@@ -5340,6 +5352,9 @@ copyObjectImpl(const void *from)
case T_TransactionStmt:
retval = _copyTransactionStmt(from);
break;
+ case T_WaitClause:
+ retval = _copyWaitClause(from);
+ break;
case T_CompositeTypeStmt:
retval = _copyCompositeTypeStmt(from);
break;
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index 627b026b195..ecad865771a 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -1542,6 +1542,16 @@ _equalTransactionStmt(const TransactionStmt *a, const TransactionStmt *b)
COMPARE_STRING_FIELD(savepoint_name);
COMPARE_STRING_FIELD(gid);
COMPARE_SCALAR_FIELD(chain);
+ COMPARE_NODE_FIELD(wait);
+
+ return true;
+}
+
+static bool
+_equalWaitClause(const WaitClause *a, const WaitClause *b)
+{
+ COMPARE_STRING_FIELD(lsn);
+ COMPARE_SCALAR_FIELD(timeout);
return true;
}
@@ -3392,6 +3402,9 @@ equal(const void *a, const void *b)
case T_TransactionStmt:
retval = _equalTransactionStmt(a, b);
break;
+ case T_WaitClause:
+ retval = _equalWaitClause(a, b);
+ break;
case T_CompositeTypeStmt:
retval = _equalCompositeTypeStmt(a, b);
break;
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index f1883847077..8455f991b18 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -2788,6 +2788,28 @@ _outDefElem(StringInfo str, const DefElem *node)
WRITE_LOCATION_FIELD(location);
}
+static void
+_outTransactionStmt(StringInfo str, const TransactionStmt *node)
+{
+ WRITE_NODE_TYPE("TRANSACTIONSTMT");
+
+ WRITE_STRING_FIELD(savepoint_name);
+ WRITE_STRING_FIELD(gid);
+ WRITE_NODE_FIELD(options);
+ WRITE_BOOL_FIELD(chain);
+ WRITE_ENUM_FIELD(kind, TransactionStmtKind);
+ WRITE_NODE_FIELD(wait);
+}
+
+static void
+_outWaitClause(StringInfo str, const WaitClause *node)
+{
+ WRITE_NODE_TYPE("WAITCLAUSE");
+
+ WRITE_STRING_FIELD(lsn);
+ WRITE_UINT_FIELD(timeout);
+}
+
static void
_outTableLikeClause(StringInfo str, const TableLikeClause *node)
{
@@ -4338,6 +4360,12 @@ outNode(StringInfo str, const void *obj)
case T_PartitionRangeDatum:
_outPartitionRangeDatum(str, obj);
break;
+ case T_TransactionStmt:
+ _outTransactionStmt(str, obj);
+ break;
+ case T_WaitClause:
+ _outWaitClause(str, obj);
+ break;
default:
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 67483552441..6c24f518acc 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -600,6 +600,8 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
%type <partboundspec> PartitionBoundSpec
%type <list> hash_partbound
%type <defelt> hash_partbound_elem
+%type <ival> wait_time
+%type <node> begin_after
/*
* Non-keyword token types. These are hard-wired into the "flex" lexer.
@@ -710,7 +712,8 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
VACUUM VALID VALIDATE VALIDATOR VALUE_P VALUES VARCHAR VARIADIC VARYING
VERBOSE VERSION_P VIEW VIEWS VOLATILE
- WHEN WHERE WHITESPACE_P WINDOW WITH WITHIN WITHOUT WORK WRAPPER WRITE
+ WHEN WHERE WHITESPACE_P WINDOW
+ WITH WITHIN WITHOUT WORK WRAPPER WRITE
XML_P XMLATTRIBUTES XMLCONCAT XMLELEMENT XMLEXISTS XMLFOREST XMLNAMESPACES
XMLPARSE XMLPI XMLROOT XMLSERIALIZE XMLTABLE
@@ -9960,18 +9963,20 @@ TransactionStmt:
n->chain = $3;
$$ = (Node *)n;
}
- | BEGIN_P opt_transaction transaction_mode_list_or_empty
+ | BEGIN_P opt_transaction transaction_mode_list_or_empty begin_after
{
TransactionStmt *n = makeNode(TransactionStmt);
n->kind = TRANS_STMT_BEGIN;
n->options = $3;
+ n->wait = $4;
$$ = (Node *)n;
}
- | START TRANSACTION transaction_mode_list_or_empty
+ | START TRANSACTION transaction_mode_list_or_empty begin_after
{
TransactionStmt *n = makeNode(TransactionStmt);
n->kind = TRANS_STMT_START;
n->options = $3;
+ n->wait = $4;
$$ = (Node *)n;
}
| COMMIT opt_transaction opt_transaction_chain
@@ -14259,6 +14264,25 @@ xml_passing_mech:
| BY VALUE_P
;
+/*
+ * AFTER clause of BEGIN and START TRANSACTION statements
+ */
+begin_after:
+ AFTER Sconst wait_time
+ {
+ WaitClause *n = makeNode(WaitClause);
+ n->lsn = $2;
+ n->timeout = $3;
+ $$ = (Node *)n;
+ }
+ | /* EMPTY */ { $$ = NULL; }
+ ;
+
+wait_time:
+ WITHIN Iconst { $$ = $2; }
+ | /* EMPTY */ { $$ = 0; }
+ ;
+
/*
* Aggregate decoration clauses
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 427b0d59cde..abc93295478 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -22,6 +22,7 @@
#include "access/subtrans.h"
#include "access/twophase.h"
#include "commands/async.h"
+#include "commands/wait.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "postmaster/autovacuum.h"
@@ -147,6 +148,7 @@ CreateSharedMemoryAndSemaphores(void)
size = add_size(size, BTreeShmemSize());
size = add_size(size, SyncScanShmemSize());
size = add_size(size, AsyncShmemSize());
+ size = add_size(size, WaitShmemSize());
#ifdef EXEC_BACKEND
size = add_size(size, ShmemBackendArraySize());
#endif
@@ -264,6 +266,11 @@ CreateSharedMemoryAndSemaphores(void)
SyncScanShmemInit();
AsyncShmemInit();
+ /*
+ * Init array of events for the BEGIN AFTER clause in shared memory
+ */
+ WaitShmemInit();
+
#ifdef EXEC_BACKEND
/*
diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index f79fa687b73..94f1df64af1 100644
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -38,6 +38,7 @@
#include "access/transam.h"
#include "access/twophase.h"
#include "access/xact.h"
+#include "commands/wait.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "postmaster/autovacuum.h"
@@ -720,6 +721,9 @@ LockErrorCleanup(void)
AbortStrongLockAcquire();
+ /* If BEGIN AFTER was interrupted, then stop waiting for that LSN */
+ DeleteWaitedLSN();
+
/* Nothing to do if we weren't waiting for a lock */
if (lockAwaited == NULL)
{
diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
index 0070dfa5b82..022816cbbb9 100644
--- a/src/backend/tcop/utility.c
+++ b/src/backend/tcop/utility.c
@@ -57,6 +57,7 @@
#include "commands/user.h"
#include "commands/vacuum.h"
#include "commands/view.h"
+#include "commands/wait.h"
#include "miscadmin.h"
#include "parser/parse_utilcmd.h"
#include "postmaster/bgwriter.h"
@@ -593,6 +594,18 @@ standard_ProcessUtility(PlannedStmt *pstmt,
case TRANS_STMT_START:
{
ListCell *lc;
+ WaitClause *waitstmt = (WaitClause *) stmt->wait;
+
+ /* BEGIN AFTER cannot be used on primary */
+ if (stmt->wait && !RecoveryInProgress())
+ ereport(ERROR,
+ (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ errmsg("BEGIN AFTER can only be "
+ "used on standby")));
+
+ /* If needed to BEGIN AFTER something but failed */
+ if (stmt->wait && WaitMain(waitstmt, dest) == 0)
+ break;
BeginTransactionBlock();
foreach(lc, stmt->options)
diff --git a/src/backend/utils/adt/misc.c b/src/backend/utils/adt/misc.c
index 37c23c9155a..2181191d99e 100644
--- a/src/backend/utils/adt/misc.c
+++ b/src/backend/utils/adt/misc.c
@@ -373,8 +373,6 @@ pg_sleep(PG_FUNCTION_ARGS)
* less than the specified time when WaitLatch is terminated early by a
* non-query-canceling signal such as SIGHUP.
*/
-#define GetNowFloat() ((float8) GetCurrentTimestamp() / 1000000.0)
-
endtime = GetNowFloat() + secs;
for (;;)
diff --git a/src/include/commands/wait.h b/src/include/commands/wait.h
new file mode 100644
index 00000000000..d08ee574ed3
--- /dev/null
+++ b/src/include/commands/wait.h
@@ -0,0 +1,27 @@
+/*-------------------------------------------------------------------------
+ *
+ * wait.h
+ * prototypes for commands/wait.c
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 2020, Regents of PostgresPro
+ *
+ * src/include/commands/wait.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef WAIT_H
+#define WAIT_H
+#include "postgres.h"
+#include "tcop/dest.h"
+#include "nodes/parsenodes.h"
+
+extern bool WaitUtility(XLogRecPtr lsn, const int timeout_ms);
+extern Size WaitShmemSize(void);
+extern void WaitShmemInit(void);
+extern void WaitSetLatch(XLogRecPtr cur_lsn);
+extern XLogRecPtr GetMinWaitedLSN(void);
+extern int WaitMain(WaitClause *stmt, DestReceiver *dest);
+extern void DeleteWaitedLSN(void);
+
+#endif /* WAIT_H */
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index 381d84b4e4f..822827aa32d 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -492,6 +492,7 @@ typedef enum NodeTag
T_StartReplicationCmd,
T_TimeLineHistoryCmd,
T_SQLCmd,
+ T_WaitClause,
/*
* TAGS FOR RANDOM OTHER STUFF
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index ada17bf6eea..7d8c1fdcf92 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -1431,6 +1431,17 @@ typedef struct OnConflictClause
int location; /* token location, or -1 if unknown */
} OnConflictClause;
+/*
+ * WaitClause -
+ * representation of WAIT FOR clause for BEGIN and START TRANSACTION.
+ */
+typedef struct WaitClause
+{
+ NodeTag type;
+ char *lsn; /* LSN to wait for */
+ int timeout; /* Number of milliseconds to limit wait time */
+} WaitClause;
+
/*
* CommonTableExpr -
* representation of WITH list element
@@ -3062,6 +3073,7 @@ typedef struct TransactionStmt
char *savepoint_name; /* for savepoint commands */
char *gid; /* for two-phase-commit related commands */
bool chain; /* AND CHAIN option */
+ Node *wait; /* BEGIN AFTER clause */
} TransactionStmt;
/* ----------------------
diff --git a/src/include/utils/timestamp.h b/src/include/utils/timestamp.h
index 03a1de569f0..eaeeb79c411 100644
--- a/src/include/utils/timestamp.h
+++ b/src/include/utils/timestamp.h
@@ -109,4 +109,6 @@ extern int date2isoyearday(int year, int mon, int mday);
extern bool TimestampTimestampTzRequiresRewrite(void);
+#define GetNowFloat() ((float8) GetCurrentTimestamp() / 1000000.0)
+
#endif /* TIMESTAMP_H */
diff --git a/src/test/recovery/t/021_begin_after.pl b/src/test/recovery/t/021_begin_after.pl
new file mode 100644
index 00000000000..1e3570d7633
--- /dev/null
+++ b/src/test/recovery/t/021_begin_after.pl
@@ -0,0 +1,85 @@
+# Checks BEGIN AFTER
+use strict;
+use warnings;
+
+use PostgresNode;
+use TestLib;
+use Test::More tests => 8;
+
+# Initialize primary node
+my $node_primary = get_new_node('primary');
+$node_primary->init(allows_streaming => 1);
+$node_primary->start;
+
+# And some content and take a backup
+$node_primary->safe_psql('postgres',
+ "CREATE TABLE wait_test AS SELECT generate_series(1,10) AS a");
+my $backup_name = 'my_backup';
+$node_primary->backup($backup_name);
+
+# Using the backup, create a streaming standby with a 1 second delay
+my $node_standby = get_new_node('standby');
+my $delay = 1;
+$node_standby->init_from_backup($node_primary, $backup_name,
+ has_streaming => 1);
+$node_standby->append_conf('postgresql.conf', qq[
+ recovery_min_apply_delay = '${delay}s'
+]);
+$node_standby->start;
+
+
+# Check that within makes us wait for the specified time (1s here)
+my $current_time = $node_standby->safe_psql('postgres', "SELECT now()");
+my $two_seconds = 2000; # in milliseconds
+my $start_time = time();
+$node_standby->safe_psql('postgres',
+ "BEGIN AFTER '0/FFFFFFFF' WITHIN $two_seconds");
+my $time_waited = (time() - $start_time) * 1000; # convert to milliseconds
+ok($time_waited >= $two_seconds, "BEGIN AFTER WITHIN waits for enough time");
+
+
+# Check that within lets us stop waiting right away, before reaching target LSN
+$node_primary->safe_psql('postgres',
+ "INSERT INTO wait_test VALUES (generate_series(11, 20))");
+my $lsn1 = $node_primary->safe_psql('postgres', "SELECT pg_current_wal_lsn()");
+my ($ret, $out, $err) = $node_standby->psql('postgres',
+ "BEGIN AFTER '$lsn1' WITHIN 1");
+
+ok($ret == 0, "zero return value when failed to BEGIN AFTER on standby");
+ok($err =~ /WARNING: didn't start transaction because LSN was not reached/,
+ "correct error message when failed to BEGIN AFTER on standby");
+ok($out eq "f", "if given too little wait time, WAIT doesn't reach target LSN");
+
+
+# Check that BEGIN AFTER works fine and reaches target LSN if given no within
+
+# Add data on primary, memorize primary's last LSN
+$node_primary->safe_psql('postgres',
+ "INSERT INTO wait_test VALUES (generate_series(21, 30))");
+my $lsn2 = $node_primary->safe_psql('postgres', "SELECT pg_current_wal_lsn()");
+
+# Wait for it to appear on replica, memorize replica's last LSN
+$node_standby->safe_psql('postgres',
+ "BEGIN AFTER '$lsn2'");
+my $reached_lsn = $node_standby->safe_psql('postgres',
+ "SELECT pg_last_wal_replay_lsn()");
+
+# Make sure that primary's and replica's LSNs are the same after WAIT
+my $compare_lsns = $node_standby->safe_psql('postgres',
+ "SELECT pg_lsn_cmp('$reached_lsn'::pg_lsn, '$lsn2'::pg_lsn)");
+ok($compare_lsns eq 0,
+ "standby reached the same LSN as primary before starting transaction");
+
+
+# Make sure that it's not allowed to use BEGIN AFTER on primary
+($ret, $out, $err) = $node_primary->psql('postgres',
+ "BEGIN AFTER '0/FFFFFFFF'");
+
+ok($ret != 0, "non-zero return value when trying to BEGIN AFTER on primary");
+ok($err =~ /ERROR: BEGIN AFTER can only be used on standby/,
+ "correct error message when trying to BEGIN AFTER on primary");
+ok($out eq '', "empty output when trying to BEGIN AFTER on primary");
+
+
+$node_standby->stop;
+$node_primary->stop;
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 7eaaad1e140..652e83b550f 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2678,6 +2678,7 @@ WSABUF
WSADATA
WSANETWORKEVENTS
WSAPROTOCOL_INFO
+WaitClause
WaitEvent
WaitEventActivity
WaitEventClient
@@ -2686,6 +2687,7 @@ WaitEventIPC
WaitEventSet
WaitEventTimeout
WaitPMResult
+WaitState
WalCloseMethod
WalLevel
WalRcvData
