Clean-ups for 776621a5e4 and 7329240437.

Following are a few clean-ups related to failover option support in slots:
1. Improve the documentation in create_subscription.sgml.
2. Remove the spurious blank line in subscriptioncmds.c.
3. Remove the NOTICE for alter_replication_slot in subscriptioncmds.c as
we would sometimes print it even when nothing has changed. One can find
the change by enabling log_replication_commands on the publisher.
4. Optimize ReplicationSlotAlter() function to prevent disk flushing when
the slot's data remains unchanged.

Author: Hou Zhijie
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/514f6f2f-6833-4539-39f1-96cd1e011f23@enterprisedb.com
Discussion: https://postgr.es/m/OS0PR01MB57164904651FB588A518E98894472@OS0PR01MB5716.jpnprd01.prod.outlook.com

doc/src/sgml/ref/create_subscription.sgml

@@ -117,9 +117,8 @@ CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceabl
           command should connect to the publisher at all.  The default
           is <literal>true</literal>.  Setting this to
           <literal>false</literal> will force the values of
-          <literal>create_slot</literal>, <literal>enabled</literal>,
-          <literal>copy_data</literal>, and <literal>failover</literal>
-          to <literal>false</literal>.
+          <literal>create_slot</literal>, <literal>enabled</literal> and
+          <literal>copy_data</literal> to <literal>false</literal>.
           (You cannot combine setting <literal>connect</literal>
           to <literal>false</literal> with
           setting <literal>create_slot</literal>, <literal>enabled</literal>,

doc/src/sgml/ref/pg_dump.sgml

@@ -1591,9 +1591,7 @@ CREATE DATABASE foo WITH TEMPLATE template0;
    information might have to be changed.  If the subscription needs to
    be enabled for
    <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>,
-   then same needs to be done by executing
-   <link linkend="sql-altersubscription-params-set">
-   <literal>ALTER SUBSCRIPTION ... SET (failover = true)</literal></link>
+   execute <link linkend="sql-altersubscription-params-set"><literal>ALTER SUBSCRIPTION ... SET (failover = true)</literal></link>
    after the slot has been created.  It might also be appropriate to
    truncate the target tables before initiating a new full table copy.  If users
    intend to copy initial data during refresh they must create the slot with

src/backend/access/transam/clog.c

@@ -766,14 +766,10 @@ StartupCLOG(void)
 	TransactionId xid = XidFromFullTransactionId(TransamVariables->nextXid);
 	int64		pageno = TransactionIdToPage(xid);
 
-	LWLockAcquire(XactSLRULock, LW_EXCLUSIVE);
-
 	/*
 	 * Initialize our idea of the latest page number.
 	 */
-	XactCtl->shared->latest_page_number = pageno;
-
-	LWLockRelease(XactSLRULock);
+	pg_atomic_write_u64(&XactCtl->shared->latest_page_number, pageno);
 }
 
 /*

src/backend/access/transam/commit_ts.c

@@ -689,9 +689,7 @@ ActivateCommitTs(void)
 	/*
 	 * Re-Initialize our idea of the latest page number.
 	 */
-	LWLockAcquire(CommitTsSLRULock, LW_EXCLUSIVE);
-	CommitTsCtl->shared->latest_page_number = pageno;
-	LWLockRelease(CommitTsSLRULock);
+	pg_atomic_write_u64(&CommitTsCtl->shared->latest_page_number, pageno);
 
 	/*
 	 * If CommitTs is enabled, but it wasn't in the previous server run, we
@@ -1006,7 +1004,8 @@ commit_ts_redo(XLogReaderState *record)
 		 * During XLOG replay, latest_page_number isn't set up yet; insert a
 		 * suitable value to bypass the sanity test in SimpleLruTruncate.
 		 */
-		CommitTsCtl->shared->latest_page_number = trunc->pageno;
+		pg_atomic_write_u64(&CommitTsCtl->shared->latest_page_number,
+							trunc->pageno);
 
 		SimpleLruTruncate(CommitTsCtl, trunc->pageno);
 	}

src/backend/access/transam/multixact.c

@@ -2017,13 +2017,15 @@ StartupMultiXact(void)
 	 * Initialize offset's idea of the latest page number.
 	 */
 	pageno = MultiXactIdToOffsetPage(multi);
-	MultiXactOffsetCtl->shared->latest_page_number = pageno;
+	pg_atomic_write_u64(&MultiXactOffsetCtl->shared->latest_page_number,
+						pageno);
 
 	/*
 	 * Initialize member's idea of the latest page number.
 	 */
 	pageno = MXOffsetToMemberPage(offset);
-	MultiXactMemberCtl->shared->latest_page_number = pageno;
+	pg_atomic_write_u64(&MultiXactMemberCtl->shared->latest_page_number,
+						pageno);
 }
 
 /*
@@ -2047,14 +2049,15 @@ TrimMultiXact(void)
 	oldestMXactDB = MultiXactState->oldestMultiXactDB;
 	LWLockRelease(MultiXactGenLock);
 
-	/* Clean up offsets state */
-	LWLockAcquire(MultiXactOffsetSLRULock, LW_EXCLUSIVE);
-
 	/*
 	 * (Re-)Initialize our idea of the latest page number for offsets.
 	 */
 	pageno = MultiXactIdToOffsetPage(nextMXact);
-	MultiXactOffsetCtl->shared->latest_page_number = pageno;
+	pg_atomic_write_u64(&MultiXactOffsetCtl->shared->latest_page_number,
+						pageno);
+
+	/* Clean up offsets state */
+	LWLockAcquire(MultiXactOffsetSLRULock, LW_EXCLUSIVE);
 
 	/*
 	 * Zero out the remainder of the current offsets page.  See notes in
@@ -2081,14 +2084,16 @@ TrimMultiXact(void)
 
 	LWLockRelease(MultiXactOffsetSLRULock);
 
-	/* And the same for members */
-	LWLockAcquire(MultiXactMemberSLRULock, LW_EXCLUSIVE);
-
 	/*
+	 * And the same for members.
+	 *
 	 * (Re-)Initialize our idea of the latest page number for members.
 	 */
 	pageno = MXOffsetToMemberPage(offset);
-	MultiXactMemberCtl->shared->latest_page_number = pageno;
+	pg_atomic_write_u64(&MultiXactMemberCtl->shared->latest_page_number,
+						pageno);
+
+	LWLockAcquire(MultiXactMemberSLRULock, LW_EXCLUSIVE);
 
 	/*
 	 * Zero out the remainder of the current members page.  See notes in
@@ -3333,7 +3338,8 @@ multixact_redo(XLogReaderState *record)
 		 * SimpleLruTruncate.
 		 */
 		pageno = MultiXactIdToOffsetPage(xlrec.endTruncOff);
-		MultiXactOffsetCtl->shared->latest_page_number = pageno;
+		pg_atomic_write_u64(&MultiXactOffsetCtl->shared->latest_page_number,
+							pageno);
 		PerformOffsetsTruncation(xlrec.startTruncOff, xlrec.endTruncOff);
 
 		LWLockRelease(MultiXactTruncationLock);

src/backend/access/transam/slru.c

@@ -17,7 +17,8 @@
  * per-buffer LWLocks that synchronize I/O for each buffer.  The control lock
  * must be held to examine or modify any shared state.  A process that is
  * reading in or writing out a page buffer does not hold the control lock,
- * only the per-buffer lock for the buffer it is working on.
+ * only the per-buffer lock for the buffer it is working on.  One exception
+ * is latest_page_number, which is read and written using atomic ops.
  *
  * "Holding the control lock" means exclusive lock in all cases except for
  * SimpleLruReadPage_ReadOnly(); see comments for SlruRecentlyUsed() for
@@ -239,8 +240,7 @@ SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns,
 		shared->lsn_groups_per_page = nlsns;
 
 		shared->cur_lru_count = 0;
-
-		/* shared->latest_page_number will be set later */
+		pg_atomic_init_u64(&shared->latest_page_number, 0);
 
 		shared->slru_stats_idx = pgstat_get_slru_index(name);
 
@@ -329,8 +329,15 @@ SimpleLruZeroPage(SlruCtl ctl, int64 pageno)
 	/* Set the LSNs for this new page to zero */
 	SimpleLruZeroLSNs(ctl, slotno);
 
-	/* Assume this page is now the latest active page */
-	shared->latest_page_number = pageno;
+	/*
+	 * Assume this page is now the latest active page.
+	 *
+	 * Note that because both this routine and SlruSelectLRUPage run with
+	 * ControlLock held, it is not possible for this to be zeroing a page that
+	 * SlruSelectLRUPage is going to evict simultaneously.  Therefore, there's
+	 * no memory barrier here.
+	 */
+	pg_atomic_write_u64(&shared->latest_page_number, pageno);
 
 	/* update the stats counter of zeroed pages */
 	pgstat_count_slru_page_zeroed(shared->slru_stats_idx);
@@ -1113,9 +1120,17 @@ SlruSelectLRUPage(SlruCtl ctl, int64 pageno)
 				shared->page_lru_count[slotno] = cur_count;
 				this_delta = 0;
 			}
+
+			/*
+			 * If this page is the one most recently zeroed, don't consider it
+			 * an eviction candidate. See comments in SimpleLruZeroPage for an
+			 * explanation about the lack of a memory barrier here.
+			 */
 			this_page_number = shared->page_number[slotno];
-			if (this_page_number == shared->latest_page_number)
+			if (this_page_number ==
+				pg_atomic_read_u64(&shared->latest_page_number))
 				continue;
+
 			if (shared->page_status[slotno] == SLRU_PAGE_VALID)
 			{
 				if (this_delta > best_valid_delta ||
@@ -1254,7 +1269,6 @@ void
 SimpleLruTruncate(SlruCtl ctl, int64 cutoffPage)
 {
 	SlruShared	shared = ctl->shared;
-	int			slotno;
 
 	/* update the stats counter of truncates */
 	pgstat_count_slru_truncate(shared->slru_stats_idx);
@@ -1270,10 +1284,13 @@ SimpleLruTruncate(SlruCtl ctl, int64 cutoffPage)
 restart:
 
 	/*
-	 * While we are holding the lock, make an important safety check: the
-	 * current endpoint page must not be eligible for removal.
+	 * An important safety check: the current endpoint page must not be
+	 * eligible for removal.  This check is just a backstop against wraparound
+	 * bugs elsewhere in SLRU handling, so we don't care if we read a slightly
+	 * outdated value; therefore we don't add a memory barrier.
 	 */
-	if (ctl->PagePrecedes(shared->latest_page_number, cutoffPage))
+	if (ctl->PagePrecedes(pg_atomic_read_u64(&shared->latest_page_number),
+						  cutoffPage))
 	{
 		LWLockRelease(shared->ControlLock);
 		ereport(LOG,
@@ -1282,7 +1299,7 @@ restart:
 		return;
 	}
 
-	for (slotno = 0; slotno < shared->num_slots; slotno++)
+	for (int slotno = 0; slotno < shared->num_slots; slotno++)
 	{
 		if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
 			continue;

src/backend/catalog/namespace.c

@@ -256,7 +256,7 @@ spcachekey_hash(SearchPathCacheKey key)
 	fasthash_state hs;
 	int			sp_len;
 
-	fasthash_init(&hs, FH_UNKNOWN_LENGTH, 0);
+	fasthash_init(&hs, 0);
 
 	hs.accum = key.roleid;
 	fasthash_combine(&hs);

src/backend/commands/copyto.c

@@ -54,14 +54,6 @@ typedef enum CopyDest
 	COPY_CALLBACK,				/* to callback function */
 } CopyDest;
 
-/*
- * Per-format callback to send output representation of one attribute for
- * a `string`.  `use_quote` tracks if quotes are required in the output
- * representation.
- */
-typedef void (*CopyAttributeOut) (CopyToState cstate, const char *string,
-								  bool use_quote);
-
 /*
  * This struct contains all the state variables used throughout a COPY TO
  * operation.
@@ -105,7 +97,6 @@ typedef struct CopyToStateData
 	MemoryContext copycontext;	/* per-copy execution context */
 
 	FmgrInfo   *out_functions;	/* lookup info for output functions */
-	CopyAttributeOut copy_attribute_out;	/* output representation callback */
 	MemoryContext rowcontext;	/* per-row evaluation context */
 	uint64		bytes_processed;	/* number of bytes processed so far */
 } CopyToStateData;
@@ -126,10 +117,7 @@ static const char BinarySignature[11] = "PGCOPY\n\377\r\n\0";
 static void EndCopy(CopyToState cstate);
 static void ClosePipeToProgram(CopyToState cstate);
 static void CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot);
-
-/* Callbacks for copy_attribute_out */
-static void CopyAttributeOutText(CopyToState cstate, const char *string,
-								 bool use_quote);
+static void CopyAttributeOutText(CopyToState cstate, const char *string);
 static void CopyAttributeOutCSV(CopyToState cstate, const char *string,
 								bool use_quote);
 
@@ -445,15 +433,6 @@ BeginCopyTo(ParseState *pstate,
 	/* Extract options from the statement node tree */
 	ProcessCopyOptions(pstate, &cstate->opts, false /* is_from */ , options);
 
-	/* Set output representation callback */
-	if (!cstate->opts.binary)
-	{
-		if (cstate->opts.csv_mode)
-			cstate->copy_attribute_out = CopyAttributeOutCSV;
-		else
-			cstate->copy_attribute_out = CopyAttributeOutText;
-	}
-
 	/* Process the source/target relation or query */
 	if (rel)
 	{
@@ -857,8 +836,10 @@ DoCopyTo(CopyToState cstate)
 
 				colname = NameStr(TupleDescAttr(tupDesc, attnum - 1)->attname);
 
-				/* Ignore quotes */
-				cstate->copy_attribute_out(cstate, colname, false);
+				if (cstate->opts.csv_mode)
+					CopyAttributeOutCSV(cstate, colname, false);
+				else
+					CopyAttributeOutText(cstate, colname);
 			}
 
 			CopySendEndOfRow(cstate);
@@ -968,9 +949,11 @@ CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot)
 			{
 				string = OutputFunctionCall(&out_functions[attnum - 1],
 											value);
-
-				cstate->copy_attribute_out(cstate, string,
-										   cstate->opts.force_quote_flags[attnum - 1]);
+				if (cstate->opts.csv_mode)
+					CopyAttributeOutCSV(cstate, string,
+										cstate->opts.force_quote_flags[attnum - 1]);
+				else
+					CopyAttributeOutText(cstate, string);
 			}
 			else
 			{
@@ -1000,8 +983,7 @@ CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot)
 	} while (0)
 
 static void
-CopyAttributeOutText(CopyToState cstate, const char *string,
-					 bool use_quote)
+CopyAttributeOutText(CopyToState cstate, const char *string)
 {
 	const char *ptr;
 	const char *start;

src/backend/commands/subscriptioncmds.c

@@ -73,7 +73,6 @@
 #define SUBOPT_LSN					0x00004000
 #define SUBOPT_ORIGIN				0x00008000
 
-
 /* check if the 'val' has 'bits' set */
 #define IsSet(val, bits)  (((val) & (bits)) == (bits))
 
@@ -852,9 +851,6 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 					 (opts.failover || walrcv_server_version(wrconn) >= 170000))
 			{
 				walrcv_alter_slot(wrconn, opts.slot_name, opts.failover);
-				ereport(NOTICE,
-						(errmsg("changed the failover state of replication slot \"%s\" on publisher to %s",
-								opts.slot_name, opts.failover ? "true" : "false")));
 			}
 		}
 		PG_FINALLY();
@@ -1547,10 +1543,6 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 		PG_TRY();
 		{
 			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
-
-			ereport(NOTICE,
-					(errmsg("changed the failover state of replication slot \"%s\" on publisher to %s",
-							sub->slotname, opts.failover ? "true" : "false")));
 		}
 		PG_FINALLY();
 		{

src/backend/replication/slot.c

@@ -696,12 +696,16 @@ ReplicationSlotAlter(const char *name, bool failover)
 				errmsg("cannot use %s with a physical replication slot",
 					   "ALTER_REPLICATION_SLOT"));
 
-	SpinLockAcquire(&MyReplicationSlot->mutex);
-	MyReplicationSlot->data.failover = failover;
-	SpinLockRelease(&MyReplicationSlot->mutex);
+	if (MyReplicationSlot->data.failover != failover)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.failover = failover;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		ReplicationSlotMarkDirty();
+		ReplicationSlotSave();
+	}
 
-	ReplicationSlotMarkDirty();
-	ReplicationSlotSave();
 	ReplicationSlotRelease();
 }
 

src/include/access/slru.h

@@ -49,6 +49,9 @@ typedef enum
 
 /*
  * Shared-memory state
+ *
+ * ControlLock is used to protect access to the other fields, except
+ * latest_page_number, which uses atomics; see comment in slru.c.
  */
 typedef struct SlruSharedData
 {
@@ -95,7 +98,7 @@ typedef struct SlruSharedData
 	 * this is not critical data, since we use it only to avoid swapping out
 	 * the latest page.
 	 */
-	int64		latest_page_number;
+	pg_atomic_uint64 latest_page_number;
 
 	/* SLRU's index for statistics purposes (might not be unique) */
 	int			slru_stats_idx;

src/include/common/hashfn_unstable.h

@@ -53,27 +53,40 @@
  * fasthash as implemented here has two interfaces:
  *
  * 1) Standalone functions, e.g. fasthash32() for a single value with a
- * known length.
+ * known length. These return the same hash code as the original, at
+ * least on little-endian machines.
  *
  * 2) Incremental interface. This can used for incorporating multiple
- * inputs. The standalone functions use this internally, so see fasthash64()
- * for an an example of how this works.
- *
- * The incremental interface is especially useful if any of the inputs
- * are NUL-terminated C strings, since the length is not needed ahead
- * of time. This avoids needing to call strlen(). This case is optimized
- * in fasthash_accum_cstring() :
+ * inputs. First, initialize the hash state (here with a zero seed):
  *
  * fasthash_state hs;
- * fasthash_init(&hs, FH_UNKNOWN_LENGTH, 0);
- * len = fasthash_accum_cstring(&hs, *str);
- * ...
- * return fasthash_final32(&hs, len);
+ * fasthash_init(&hs, 0);
  *
- * Here we pass FH_UNKNOWN_LENGTH as a convention, since passing zero
- * would zero out the internal seed as well. fasthash_accum_cstring()
- * returns the length of the string, which is computed on-the-fly while
- * mixing the string into the hash. Experimentation has found that
+ * If the inputs are of types that can be trivially cast to uint64, it's
+ * sufficient to do:
+ *
+ * hs.accum = value1;
+ * fasthash_combine(&hs);
+ * hs.accum = value2;
+ * fasthash_combine(&hs);
+ * ...
+ *
+ * For longer or variable-length input, fasthash_accum() is a more
+ * flexible, but more verbose method. The standalone functions use this
+ * internally, so see fasthash64() for an an example of this.
+ *
+ * After all inputs have been mixed in, finalize the hash:
+ *
+ * hashcode = fasthash_final32(&hs, 0);
+ *
+ * The incremental interface allows an optimization for NUL-terminated
+ * C strings:
+ *
+ * len = fasthash_accum_cstring(&hs, str);
+ * hashcode = fasthash_final32(&hs, len);
+ *
+ * By handling the terminator on-the-fly, we can avoid needing a strlen()
+ * call to tell us how many bytes to hash. Experimentation has found that
  * SMHasher fails unless we incorporate the length, so it is passed to
  * the finalizer as a tweak.
  */
@@ -89,20 +102,17 @@ typedef struct fasthash_state
 
 #define FH_SIZEOF_ACCUM sizeof(uint64)
 
-#define FH_UNKNOWN_LENGTH 1
 
 /*
  * Initialize the hash state.
  *
- * 'len' is the length of the input, if known ahead of time.
- * If that is not known, pass FH_UNKNOWN_LENGTH.
  * 'seed' can be zero.
  */
 static inline void
-fasthash_init(fasthash_state *hs, int len, uint64 seed)
+fasthash_init(fasthash_state *hs, uint64 seed)
 {
 	memset(hs, 0, sizeof(fasthash_state));
-	hs->hash = seed ^ (len * 0x880355f21e6d1965);
+	hs->hash = seed ^ 0x880355f21e6d1965;
 }
 
 /* both the finalizer and part of the combining step */
@@ -210,26 +220,33 @@ fasthash_accum_cstring_aligned(fasthash_state *hs, const char *str)
 {
 	const char *const start = str;
 	int			remainder;
-	uint64		zero_bytes_le;
+	uint64		zero_byte_low;
 
 	Assert(PointerIsAligned(start, uint64));
+
+	/*
+	 * For every chunk of input, check for zero bytes before mixing into the
+	 * hash. The chunk with zeros must contain the NUL terminator. We arrange
+	 * so that zero_byte_low tells us not only that a zero exists, but also
+	 * where it is, so we can hash the remainder of the string.
+	 *
+	 * The haszero64 calculation will set bits corresponding to the lowest
+	 * byte where a zero exists, so that suffices for little-endian machines.
+	 * For big-endian machines, we would need bits set for the highest zero
+	 * byte in the chunk, since the trailing junk past the terminator could
+	 * contain additional zeros. haszero64 does not give us that, so we
+	 * byteswap the chunk first.
+	 */
 	for (;;)
 	{
 		uint64		chunk = *(uint64 *) str;
 
-		/*
-		 * With little-endian representation, we can use this calculation,
-		 * which sets bits in the first byte in the result word that
-		 * corresponds to a zero byte in the original word. The rest of the
-		 * bytes are indeterminate, so cannot be used on big-endian machines
-		 * without either swapping or a bytewise check.
-		 */
 #ifdef WORDS_BIGENDIAN
-		zero_bytes_le = haszero64(pg_bswap64(chunk));
+		zero_byte_low = haszero64(pg_bswap64(chunk));
 #else
-		zero_bytes_le = haszero64(chunk);
+		zero_byte_low = haszero64(chunk);
 #endif
-		if (zero_bytes_le)
+		if (zero_byte_low)
 			break;
 
 		hs->accum = chunk;
@@ -238,12 +255,11 @@ fasthash_accum_cstring_aligned(fasthash_state *hs, const char *str)
 	}
 
 	/*
-	 * For the last word, only use bytes up to the NUL for the hash. Bytes
-	 * with set bits will be 0x80, so calculate the first occurrence of a zero
-	 * byte within the input word by counting the number of trailing (because
-	 * little-endian) zeros and dividing the result by 8.
+	 * The byte corresponding to the NUL will be 0x80, so the rightmost bit
+	 * position will be in the range 7, 15, ..., 63. Turn this into byte
+	 * position by dividing by 8.
 	 */
-	remainder = pg_rightmost_one_pos64(zero_bytes_le) / BITS_PER_BYTE;
+	remainder = pg_rightmost_one_pos64(zero_byte_low) / BITS_PER_BYTE;
 	fasthash_accum(hs, str, remainder);
 	str += remainder;
 
@@ -328,7 +344,10 @@ fasthash64(const char *k, int len, uint64 seed)
 {
 	fasthash_state hs;
 
-	fasthash_init(&hs, len, seed);
+	fasthash_init(&hs, 0);
+
+	/* re-initialize the seed according to input length */
+	hs.hash = seed ^ (len * 0x880355f21e6d1965);
 
 	while (len >= FH_SIZEOF_ACCUM)
 	{