Initial work on COPY progress - take two.

contrib/Makefile

@@ -27,6 +27,7 @@ SUBDIRS = \
 		lo		\
 		ltree		\
 		oid2name	\
+		old_snapshot	\
 		pageinspect	\
 		passwordcheck	\
 		pg_buffercache	\

contrib/old_snapshot/Makefile

@@ -0,0 +1,22 @@
+# contrib/old_snapshot/Makefile
+
+MODULE_big = old_snapshot
+OBJS = \
+	$(WIN32RES) \
+	time_mapping.o
+PG_CPPFLAGS = -I$(libpq_srcdir)
+
+EXTENSION = old_snapshot
+DATA = old_snapshot--1.0.sql
+PGFILEDESC = "old_snapshot - utilities in support of old_snapshot_threshold"
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = contrib/old_snapshot
+top_builddir = ../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif

contrib/old_snapshot/old_snapshot--1.0.sql

@@ -0,0 +1,14 @@
+/* contrib/old_snapshot/old_snapshot--1.0.sql */
+
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION old_snapshot" to load this file. \quit
+
+-- Show visibility map and page-level visibility information for each block.
+CREATE FUNCTION pg_old_snapshot_time_mapping(array_offset OUT int4,
+											 end_timestamp OUT timestamptz,
+											 newest_xmin OUT xid)
+RETURNS SETOF record
+AS 'MODULE_PATHNAME', 'pg_old_snapshot_time_mapping'
+LANGUAGE C STRICT;
+
+-- XXX. Do we want REVOKE commands here?

contrib/old_snapshot/old_snapshot.control

@@ -0,0 +1,5 @@
+# old_snapshot extension
+comment = 'utilities in support of old_snapshot_threshold'
+default_version = '1.0'
+module_pathname = '$libdir/old_snapshot'
+relocatable = true

contrib/old_snapshot/time_mapping.c

@@ -0,0 +1,159 @@
+/*-------------------------------------------------------------------------
+ *
+ * time_mapping.c
+ *	  time to XID mapping information
+ *
+ * Copyright (c) 2020, PostgreSQL Global Development Group
+ *
+ *	  contrib/old_snapshot/time_mapping.c
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "funcapi.h"
+#include "storage/lwlock.h"
+#include "utils/old_snapshot.h"
+#include "utils/snapmgr.h"
+#include "utils/timestamp.h"
+
+/*
+ * Backend-private copy of the information from oldSnapshotControl which relates
+ * to the time to XID mapping, plus an index so that we can iterate.
+ *
+ * Note that the length of the xid_by_minute array is given by
+ * OLD_SNAPSHOT_TIME_MAP_ENTRIES (which is not a compile-time constant).
+ */
+typedef struct
+{
+	int				current_index;
+	int				head_offset;
+	TimestampTz		head_timestamp;
+	int				count_used;
+	TransactionId	xid_by_minute[FLEXIBLE_ARRAY_MEMBER];
+} OldSnapshotTimeMapping;
+
+#define NUM_TIME_MAPPING_COLUMNS 3
+
+PG_MODULE_MAGIC;
+PG_FUNCTION_INFO_V1(pg_old_snapshot_time_mapping);
+
+static OldSnapshotTimeMapping *GetOldSnapshotTimeMapping(void);
+static TupleDesc MakeOldSnapshotTimeMappingTupleDesc(void);
+static HeapTuple MakeOldSnapshotTimeMappingTuple(TupleDesc tupdesc,
+												 OldSnapshotTimeMapping *mapping);
+
+/*
+ * SQL-callable set-returning function.
+ */
+Datum
+pg_old_snapshot_time_mapping(PG_FUNCTION_ARGS)
+{
+	FuncCallContext *funcctx;
+	OldSnapshotTimeMapping *mapping;
+
+	if (SRF_IS_FIRSTCALL())
+	{
+		MemoryContext	oldcontext;
+
+		funcctx = SRF_FIRSTCALL_INIT();
+		oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
+		mapping = GetOldSnapshotTimeMapping();
+		funcctx->user_fctx = mapping;
+		funcctx->tuple_desc = MakeOldSnapshotTimeMappingTupleDesc();
+		MemoryContextSwitchTo(oldcontext);
+	}
+
+	funcctx = SRF_PERCALL_SETUP();
+	mapping = (OldSnapshotTimeMapping *) funcctx->user_fctx;
+
+	while (mapping->current_index < mapping->count_used)
+	{
+		HeapTuple	tuple;
+
+		tuple = MakeOldSnapshotTimeMappingTuple(funcctx->tuple_desc, mapping);
+		++mapping->current_index;
+		SRF_RETURN_NEXT(funcctx, HeapTupleGetDatum(tuple));
+	}
+
+	SRF_RETURN_DONE(funcctx);
+}
+
+/*
+ * Get the old snapshot time mapping data from shared memory.
+ */
+static OldSnapshotTimeMapping *
+GetOldSnapshotTimeMapping(void)
+{
+	OldSnapshotTimeMapping *mapping;
+
+	mapping = palloc(offsetof(OldSnapshotTimeMapping, xid_by_minute)
+					 + sizeof(TransactionId) * OLD_SNAPSHOT_TIME_MAP_ENTRIES);
+	mapping->current_index = 0;
+
+	LWLockAcquire(OldSnapshotTimeMapLock, LW_SHARED);
+	mapping->head_offset = oldSnapshotControl->head_offset;
+	mapping->head_timestamp = oldSnapshotControl->head_timestamp;
+	mapping->count_used = oldSnapshotControl->count_used;
+	for (int i = 0; i < OLD_SNAPSHOT_TIME_MAP_ENTRIES; ++i)
+		mapping->xid_by_minute[i] = oldSnapshotControl->xid_by_minute[i];
+	LWLockRelease(OldSnapshotTimeMapLock);
+
+	return mapping;
+}
+
+/*
+ * Build a tuple descriptor for the pg_old_snapshot_time_mapping() SRF.
+ */
+static TupleDesc
+MakeOldSnapshotTimeMappingTupleDesc(void)
+{
+	TupleDesc	tupdesc;
+
+	tupdesc = CreateTemplateTupleDesc(NUM_TIME_MAPPING_COLUMNS);
+
+	TupleDescInitEntry(tupdesc, (AttrNumber) 1, "array_offset",
+					   INT4OID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 2, "end_timestamp",
+					   TIMESTAMPTZOID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 3, "newest_xmin",
+					   XIDOID, -1, 0);
+
+	return BlessTupleDesc(tupdesc);
+}
+
+/*
+ * Convert one entry from the old snapshot time mapping to a HeapTuple.
+ */
+static HeapTuple
+MakeOldSnapshotTimeMappingTuple(TupleDesc tupdesc, OldSnapshotTimeMapping *mapping)
+{
+	Datum	values[NUM_TIME_MAPPING_COLUMNS];
+	bool	nulls[NUM_TIME_MAPPING_COLUMNS];
+	int		array_position;
+	TimestampTz	timestamp;
+
+	/*
+	 * Figure out the array position corresponding to the current index.
+	 *
+	 * Index 0 means the oldest entry in the mapping, which is stored at
+	 * mapping->head_offset. Index 1 means the next-oldest entry, which is a the
+	 * following index, and so on. We wrap around when we reach the end of the array.
+	 */
+	array_position = (mapping->head_offset + mapping->current_index)
+		% OLD_SNAPSHOT_TIME_MAP_ENTRIES;
+
+	/*
+	 * No explicit timestamp is stored for any entry other than the oldest one,
+	 * but each entry corresponds to 1-minute period, so we can just add.
+	 */
+	timestamp = TimestampTzPlusMilliseconds(mapping->head_timestamp,
+											mapping->current_index * 60000);
+
+	/* Initialize nulls and values arrays. */
+	memset(nulls, 0, sizeof(nulls));
+	values[0] = Int32GetDatum(array_position);
+	values[1] = TimestampTzGetDatum(timestamp);
+	values[2] = TransactionIdGetDatum(mapping->xid_by_minute[array_position]);
+
+	return heap_form_tuple(tupdesc, values, nulls);
+}

doc/src/sgml/btree.sgml

@@ -642,7 +642,7 @@ options(<replaceable>relopts</replaceable> <type>local_relopts *</type>) returns
   </para>
   <para>
    Deduplication works by periodically merging groups of duplicate
-   tuples together, forming a single posting list tuple for each
+   tuples together, forming a single <firstterm>posting list</firstterm> tuple for each
    group.  The column key value(s) only appear once in this
    representation.  This is followed by a sorted array of
    <acronym>TID</acronym>s that point to rows in the table.  This

doc/src/sgml/catalogs.sgml

@@ -7298,7 +7298,8 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
        of statistics accumulated for this statistics object by
        <xref linkend="sql-analyze"/>.
        A zero value indicates that no statistics should be collected.
-       A negative value says to use the system default statistics target.
+       A negative value says to use the maximum of the statistics targets of
+       the referenced columns, if set, or the system default statistics target.
        Positive values of <structfield>stxstattarget</structfield>
        determine the target number of <quote>most common values</quote>
        to collect.

doc/src/sgml/config.sgml

@@ -3813,7 +3813,7 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
         servers or streaming base backup clients (i.e., the maximum number of
         simultaneously running WAL sender processes). The default is
         <literal>10</literal>.  The value <literal>0</literal> means
-        replication is disabled.  Abrupt streaming client disconnection might
+        replication is disabled.  Abrupt disconnection of a streaming client might
         leave an orphaned connection slot behind until a timeout is reached,
         so this parameter should be set slightly higher than the maximum
         number of expected clients so disconnected clients can immediately
@@ -3902,9 +3902,9 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
         slots</link> are allowed to retain in the <filename>pg_wal</filename>
         directory at checkpoint time.
         If <varname>max_slot_wal_keep_size</varname> is -1 (the default),
-        replication slots retain unlimited amount of WAL files.  If
-        restart_lsn of a replication slot gets behind more than that megabytes
-        from the current LSN, the standby using the slot may no longer be able
+        replication slots may retain an unlimited amount of WAL files.  Otherwise, if
+        restart_lsn of a replication slot falls behind the current LSN by more
+        than the given size, the standby using the slot may no longer be able
         to continue replication due to removal of required WAL files. You
         can see the WAL availability of replication slots
         in <link linkend="view-pg-replication-slots">pg_replication_slots</link>.
@@ -6847,9 +6847,9 @@ log_line_prefix = '%m [%p] %q%u@%d/%a '
       </term>
       <listitem>
        <para>
-        If greater than zero, each bind parameter value reported in
-        non-error statement-logging messages is trimmed to this many bytes.
-        Zero disables logging bind parameters with statements.
+        If greater than zero, each bind parameter value logged with a
+        non-error statement-logging message is trimmed to this many bytes.
+        Zero disables logging of bind parameters for non-error statement logs.
         <literal>-1</literal> (the default) allows bind parameters to be
         logged in full.
         If this value is specified without units, it is taken as bytes.
@@ -8224,10 +8224,10 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
         a regular <command>VACUUM</command> in that it visits every page that might
         contain unfrozen XIDs or MXIDs, not just those that might contain dead
         tuples.  The default is 150 million transactions.  Although users can
-        set this value anywhere from zero to two billions, <command>VACUUM</command>
+        set this value anywhere from zero to two billion, <command>VACUUM</command>
         will silently limit the effective value to 95% of
         <xref linkend="guc-autovacuum-freeze-max-age"/>, so that a
-        periodical manual <command>VACUUM</command> has a chance to run before an
+        periodic manual <command>VACUUM</command> has a chance to run before an
         anti-wraparound autovacuum is launched for the table. For more
         information see
         <xref linkend="vacuum-for-wraparound"/>.
@@ -8271,10 +8271,10 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
         a regular <command>VACUUM</command> in that it visits every page that might
         contain unfrozen XIDs or MXIDs, not just those that might contain dead
         tuples.  The default is 150 million multixacts.
-        Although users can set this value anywhere from zero to two billions,
+        Although users can set this value anywhere from zero to two billion,
         <command>VACUUM</command> will silently limit the effective value to 95% of
         <xref linkend="guc-autovacuum-multixact-freeze-max-age"/>, so that a
-        periodical manual <command>VACUUM</command> has a chance to run before an
+        periodic manual <command>VACUUM</command> has a chance to run before an
         anti-wraparound is launched for the table.
         For more information see <xref linkend="vacuum-for-multixact-wraparound"/>.
        </para>

doc/src/sgml/contrib.sgml

@@ -116,6 +116,7 @@ CREATE EXTENSION <replaceable>module_name</replaceable>;
  &isn;
  &lo;
  &ltree;
+ &oldsnapshot;
  &pageinspect;
  &passwordcheck;
  &pgbuffercache;

doc/src/sgml/ddl.sgml

@@ -3992,7 +3992,7 @@ ALTER TABLE measurement ATTACH PARTITION measurement_y2008m02
      Before running the <command>ATTACH PARTITION</command> command, it is
      recommended to create a <literal>CHECK</literal> constraint on the table to
      be attached matching the desired partition constraint. That way,
-     the system will be able to skip the scan to validate the implicit
+     the system will be able to skip the scan which is otherwise needed to validate the implicit
      partition constraint. Without the <literal>CHECK</literal> constraint,
      the table will be scanned to validate the partition constraint while
      holding an <literal>ACCESS EXCLUSIVE</literal> lock on that partition

doc/src/sgml/filelist.sgml

@@ -129,6 +129,7 @@
 <!ENTITY lo              SYSTEM "lo.sgml">
 <!ENTITY ltree           SYSTEM "ltree.sgml">
 <!ENTITY oid2name        SYSTEM "oid2name.sgml">
+<!ENTITY oldsnapshot     SYSTEM "oldsnapshot.sgml">
 <!ENTITY pageinspect     SYSTEM "pageinspect.sgml">
 <!ENTITY passwordcheck   SYSTEM "passwordcheck.sgml">
 <!ENTITY pgbuffercache   SYSTEM "pgbuffercache.sgml">

doc/src/sgml/func.sgml

@@ -15626,11 +15626,11 @@ table2-mapping
         <literal>'use_json_null'</literal>.
        </para>
        <para>
-        <literal>jsonb_set_lax('[{"f1":1,"f2":null},2,null,3]', '{0,f1}',null)</literal>
+        <literal>jsonb_set_lax('[{"f1":1,"f2":null},2,null,3]', '{0,f1}', null)</literal>
         <returnvalue>[{"f1":null,"f2":null},2,null,3]</returnvalue>
        </para>
        <para>
-        <literal>jsonb_set_lax('[{"f1":99,"f2":null},2]', '{0,f3}',null, true, 'return_target')</literal>
+        <literal>jsonb_set_lax('[{"f1":99,"f2":null},2]', '{0,f3}', null, true, 'return_target')</literal>
         <returnvalue>[{"f1": 99, "f2": null}, 2]</returnvalue>
        </para></entry>
       </row>

doc/src/sgml/generate-errcodes-table.pl

@@ -3,8 +3,8 @@
 # Generate the errcodes-table.sgml file from errcodes.txt
 # Copyright (c) 2000-2020, PostgreSQL Global Development Group
 
-use warnings;
 use strict;
+use warnings;
 
 print
   "<!-- autogenerated from src/backend/utils/errcodes.txt, do not edit -->\n";

doc/src/sgml/libpq.sgml

@@ -1227,7 +1227,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <term><literal>connect_timeout</literal></term>
       <listitem>
       <para>
-       Maximum wait for connection, in seconds (write as a decimal integer,
+       Maximum time to wait while connecting, in seconds (write as a decimal integer,
        e.g., <literal>10</literal>).  Zero, negative, or not specified means
        wait indefinitely.  The minimum allowed timeout is 2 seconds, therefore
        a value of <literal>1</literal> is interpreted as <literal>2</literal>.

doc/src/sgml/lobj.sgml

@@ -901,8 +901,6 @@ exportFile(PGconn *conn, Oid lobjId, char *filename)
 
     lo_close(conn, lobj_fd);
     close(fd);
-
-    return;
 }
 
 static void

doc/src/sgml/logical-replication.sgml

@@ -403,7 +403,7 @@
    <listitem>
     <para>
      Replication is only supported by tables, including partitioned tables.
-     Attempts to replicate other types of relations such as views, materialized
+     Attempts to replicate other types of relations, such as views, materialized
      views, or foreign tables, will result in an error.
     </para>
    </listitem>