On 01.04.22 18:31, Peter Eisentraut wrote:
Consider that an identity sequence creates an "internal" dependency and a serial sequence creates an "auto" dependency.

An "internal" dependency means that the internal object shouldn't really be operated on directly.  (In some cases it's allowed for convenience.) So I think in that case the sequence must follow the table's persistence in all cases.  This is accomplished by setting the initial persistence to the table's, making ALTER TABLE propagate persistence changes, and prohibiting direct ALTER SEQUENCE SET.

But to make pg_upgrade work for identity sequences of unlogged tables, we need to allow ALTER SEQUENCE ... SET LOGGED on such sequences.  Which I guess is not a real problem in the end.

Here is an updated patch that fixes this pg_dump/pg_upgrade issue and also adds a few more comments and documentation sentences about what happens and what is allowed. I didn't change any behaviors; it seems we didn't have consensus to do that.

These details about how tables and sequences are linked or not are pretty easy to adjust, if people still have some qualms.
From b9f1c3cd56b73a81c9cc5f891d25c999f5ab214d Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <pe...@eisentraut.org>
Date: Sun, 3 Apr 2022 19:14:03 +0200
Subject: [PATCH v6] Unlogged sequences

Add support for unlogged sequences.  Unlike for unlogged tables, this
is not a performance feature.  It allows sequences associated with
unlogged tables to be excluded from replication.

A new subcommand ALTER SEQUENCE ... SET LOGGED/UNLOGGED is added.

An identity/serial sequence now automatically gets and follows the
persistence level (logged/unlogged) of its owning table.  (The
sequences owned by temporary tables were already temporary through the
separate mechanism in RangeVarAdjustRelationPersistence().)  But you
can still change the persistence of an owned sequence separately.
Also, pg_dump and pg_upgrade preserve the persistence of existing
sequences.

Discussion: 
https://www.postgresql.org/message-id/flat/04e12818-2f98-257c-b926-2845d74ed04f%402ndquadrant.com
---
 doc/src/sgml/ref/alter_sequence.sgml       | 12 +++++
 doc/src/sgml/ref/alter_table.sgml          |  6 +++
 doc/src/sgml/ref/create_sequence.sgml      | 23 +++++++-
 doc/src/sgml/ref/create_table.sgml         |  5 ++
 doc/src/sgml/ref/pg_dump.sgml              |  7 +--
 src/backend/commands/sequence.c            | 58 +++++++++++++++++---
 src/backend/commands/tablecmds.c           | 32 ++++++++++--
 src/backend/parser/parse_utilcmd.c         |  1 +
 src/bin/pg_dump/pg_dump.c                  | 15 +++++-
 src/bin/psql/describe.c                    |  8 ++-
 src/bin/psql/tab-complete.c                |  5 +-
 src/include/commands/sequence.h            |  1 +
 src/test/recovery/t/014_unlogged_reinit.pl | 61 +++++++++++++++++++---
 src/test/regress/expected/alter_table.out  |  4 +-
 src/test/regress/expected/sequence.out     | 20 ++++++-
 src/test/regress/sql/sequence.sql          | 10 +++-
 16 files changed, 237 insertions(+), 31 deletions(-)

diff --git a/doc/src/sgml/ref/alter_sequence.sgml 
b/doc/src/sgml/ref/alter_sequence.sgml
index 3cd9ece49f..148085d4f2 100644
--- a/doc/src/sgml/ref/alter_sequence.sgml
+++ b/doc/src/sgml/ref/alter_sequence.sgml
@@ -31,6 +31,7 @@
     [ RESTART [ [ WITH ] <replaceable class="parameter">restart</replaceable> 
] ]
     [ CACHE <replaceable class="parameter">cache</replaceable> ] [ [ NO ] 
CYCLE ]
     [ OWNED BY { <replaceable 
class="parameter">table_name</replaceable>.<replaceable 
class="parameter">column_name</replaceable> | NONE } ]
+ALTER SEQUENCE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> 
SET { LOGGED | UNLOGGED }
 ALTER SEQUENCE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> 
OWNER TO { <replaceable class="parameter">new_owner</replaceable> | 
CURRENT_ROLE | CURRENT_USER | SESSION_USER }
 ALTER SEQUENCE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> 
RENAME TO <replaceable class="parameter">new_name</replaceable>
 ALTER SEQUENCE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> 
SET SCHEMA <replaceable class="parameter">new_schema</replaceable>
@@ -237,6 +238,17 @@ <title>Parameters</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><literal>SET { LOGGED | UNLOGGED }</literal></term>
+      <listitem>
+       <para>
+        This form changes the sequence from unlogged to logged or vice-versa
+        (see <xref linkend="sql-createsequence"/>).  It cannot be applied to a
+        temporary sequence.
+       </para>
+      </listitem>
+     </varlistentry>
+
    <varlistentry>
     <term><literal>OWNED BY</literal> <replaceable 
class="parameter">table_name</replaceable>.<replaceable 
class="parameter">column_name</replaceable></term>
     <term><literal>OWNED BY NONE</literal></term>
diff --git a/doc/src/sgml/ref/alter_table.sgml 
b/doc/src/sgml/ref/alter_table.sgml
index e610cbbc0e..c2a458eb5d 100644
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@ -753,6 +753,12 @@ <title>Description</title>
       (see <xref linkend="sql-createtable-unlogged"/>).  It cannot be applied
       to a temporary table.
      </para>
+
+     <para>
+      This also changes the persistence of any sequences linked to the table
+      (for identity or serial columns).  However, it is also possible to
+      change the persistence of such sequences separately.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/doc/src/sgml/ref/create_sequence.sgml 
b/doc/src/sgml/ref/create_sequence.sgml
index 20bdbc002f..a84aa5bf56 100644
--- a/doc/src/sgml/ref/create_sequence.sgml
+++ b/doc/src/sgml/ref/create_sequence.sgml
@@ -21,7 +21,7 @@
 
  <refsynopsisdiv>
 <synopsis>
-CREATE [ TEMPORARY | TEMP ] SEQUENCE [ IF NOT EXISTS ] <replaceable 
class="parameter">name</replaceable>
+CREATE [ { TEMPORARY | TEMP } | UNLOGGED ] SEQUENCE [ IF NOT EXISTS ] 
<replaceable class="parameter">name</replaceable>
     [ AS <replaceable class="parameter">data_type</replaceable> ]
     [ INCREMENT [ BY ] <replaceable class="parameter">increment</replaceable> ]
     [ MINVALUE <replaceable class="parameter">minvalue</replaceable> | NO 
MINVALUE ] [ MAXVALUE <replaceable class="parameter">maxvalue</replaceable> | 
NO MAXVALUE ]
@@ -92,6 +92,27 @@ <title>Parameters</title>
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>UNLOGGED</literal></term>
+    <listitem>
+     <para>
+      If specified, the sequence is created as an unlogged sequence.  Changes
+      to unlogged sequences are not written to the write-ahead log.  They are
+      not crash-safe: an unlogged sequence is automatically reset to its
+      initial state after a crash or unclean shutdown.  Unlogged sequences are
+      also not replicated to standby servers.
+     </para>
+
+     <para>
+      Unlike unlogged tables, unlogged sequences do not offer a significant
+      performance advantage.  This option is mainly intended for sequences
+      associated with unlogged tables via identity columns or serial columns.
+      In those cases, it usually wouldn't make sense to have the sequence
+      WAL-logged and replicated but not its associated table.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>IF NOT EXISTS</literal></term>
     <listitem>
diff --git a/doc/src/sgml/ref/create_table.sgml 
b/doc/src/sgml/ref/create_table.sgml
index 7e4ef312c0..6c9918b0a1 100644
--- a/doc/src/sgml/ref/create_table.sgml
+++ b/doc/src/sgml/ref/create_table.sgml
@@ -215,6 +215,11 @@ <title>Parameters</title>
       Any indexes created on an unlogged table are automatically unlogged as
       well.
      </para>
+
+     <para>
+      If this is specified, any sequences created together with the unlogged
+      table (for identity or serial columns) are also created as unlogged.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/doc/src/sgml/ref/pg_dump.sgml b/doc/src/sgml/ref/pg_dump.sgml
index 2f0042fd96..723b2a1a66 100644
--- a/doc/src/sgml/ref/pg_dump.sgml
+++ b/doc/src/sgml/ref/pg_dump.sgml
@@ -981,9 +981,10 @@ <title>Options</title>
       <term><option>--no-unlogged-table-data</option></term>
       <listitem>
        <para>
-        Do not dump the contents of unlogged tables.  This option has no
-        effect on whether or not the table definitions (schema) are dumped;
-        it only suppresses dumping the table data. Data in unlogged tables
+        Do not dump the contents of unlogged tables and sequences.  This
+        option has no effect on whether or not the table and sequence
+        definitions (schema) are dumped; it only suppresses dumping the table
+        and sequence data. Data in unlogged tables and sequences
         is always excluded when dumping from a standby server.
        </para>
       </listitem>
diff --git a/src/backend/commands/sequence.c b/src/backend/commands/sequence.c
index 717bb0b2aa..47f62c28d4 100644
--- a/src/backend/commands/sequence.c
+++ b/src/backend/commands/sequence.c
@@ -30,6 +30,7 @@
 #include "catalog/objectaccess.h"
 #include "catalog/pg_sequence.h"
 #include "catalog/pg_type.h"
+#include "catalog/storage_xlog.h"
 #include "commands/defrem.h"
 #include "commands/sequence.h"
 #include "commands/tablecmds.h"
@@ -95,6 +96,7 @@ static HTAB *seqhashtab = NULL; /* hash table for SeqTable 
items */
 static SeqTableData *last_used_seq = NULL;
 
 static void fill_seq_with_data(Relation rel, HeapTuple tuple);
+static void fill_seq_fork_with_data(Relation rel, HeapTuple tuple, ForkNumber 
forkNum);
 static Relation lock_and_open_sequence(SeqTable seq);
 static void create_seq_hashtable(void);
 static void init_sequence(Oid relid, SeqTable *p_elm, Relation *p_rel);
@@ -133,12 +135,6 @@ DefineSequence(ParseState *pstate, CreateSeqStmt *seq)
        bool            pgs_nulls[Natts_pg_sequence];
        int                     i;
 
-       /* Unlogged sequences are not implemented -- not clear if useful. */
-       if (seq->sequence->relpersistence == RELPERSISTENCE_UNLOGGED)
-               ereport(ERROR,
-                               (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-                                errmsg("unlogged sequences are not 
supported")));
-
        /*
         * If if_not_exists was given and a relation with the same name already
         * exists, bail out. (Note: we needn't check this when not 
if_not_exists,
@@ -492,9 +488,33 @@ SetSequence(Oid seq_relid, bool transactional, int64 
last_value, int64 log_cnt,
 
 /*
  * Initialize a sequence's relation with the specified tuple as content
+ *
+ * This handles unlogged sequences by writing to both the main and the init
+ * fork as necessary.
  */
 static void
 fill_seq_with_data(Relation rel, HeapTuple tuple)
+{
+       fill_seq_fork_with_data(rel, tuple, MAIN_FORKNUM);
+
+       if (rel->rd_rel->relpersistence == RELPERSISTENCE_UNLOGGED)
+       {
+               SMgrRelation srel;
+
+               srel = smgropen(rel->rd_node, InvalidBackendId);
+               smgrcreate(srel, INIT_FORKNUM, false);
+               log_smgrcreate(&rel->rd_node, INIT_FORKNUM);
+               fill_seq_fork_with_data(rel, tuple, INIT_FORKNUM);
+               FlushRelationBuffers(rel);
+               smgrclose(srel);
+       }
+}
+
+/*
+ * Initialize a sequence's relation fork with the specified tuple as content
+ */
+static void
+fill_seq_fork_with_data(Relation rel, HeapTuple tuple, ForkNumber forkNum)
 {
        Buffer          buf;
        Page            page;
@@ -503,7 +523,7 @@ fill_seq_with_data(Relation rel, HeapTuple tuple)
 
        /* Initialize first page of relation with special magic number */
 
-       buf = ReadBuffer(rel, P_NEW);
+       buf = ReadBufferExtended(rel, forkNum, P_NEW, RBM_NORMAL, NULL);
        Assert(BufferGetBlockNumber(buf) == 0);
 
        page = BufferGetPage(buf);
@@ -549,7 +569,7 @@ fill_seq_with_data(Relation rel, HeapTuple tuple)
                elog(ERROR, "failed to add sequence tuple to page");
 
        /* XLOG stuff */
-       if (RelationNeedsWAL(rel))
+       if (RelationNeedsWAL(rel) || forkNum == INIT_FORKNUM)
        {
                xl_seq_rec      xlrec;
                XLogRecPtr      recptr;
@@ -682,6 +702,28 @@ AlterSequence(ParseState *pstate, AlterSeqStmt *stmt)
        return address;
 }
 
+void
+SequenceChangePersistence(Oid relid, char newrelpersistence)
+{
+       SeqTable        elm;
+       Relation        seqrel;
+       Buffer          buf;
+       HeapTupleData seqdatatuple;
+
+       init_sequence(relid, &elm, &seqrel);
+
+       /* check the comment above nextval_internal()'s equivalent call. */
+       if (RelationNeedsWAL(seqrel))
+               GetTopTransactionId();
+
+       (void) read_seq_tuple(seqrel, &buf, &seqdatatuple);
+       RelationSetNewRelfilenode(seqrel, newrelpersistence);
+       fill_seq_with_data(seqrel, &seqdatatuple);
+       UnlockReleaseBuffer(buf);
+
+       relation_close(seqrel, NoLock);
+}
+
 void
 DeleteSequenceTuple(Oid relid)
 {
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 51b4a00d50..675f641b46 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -319,6 +319,7 @@ struct DropRelationCallbackState
 #define                ATT_COMPOSITE_TYPE              0x0010
 #define                ATT_FOREIGN_TABLE               0x0020
 #define                ATT_PARTITIONED_INDEX   0x0040
+#define                ATT_SEQUENCE                    0x0080
 
 /*
  * ForeignTruncateInfo
@@ -4660,7 +4661,7 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
                        pass = AT_PASS_MISC;
                        break;
                case AT_SetLogged:              /* SET LOGGED */
-                       ATSimplePermissions(cmd->subtype, rel, ATT_TABLE);
+                       ATSimplePermissions(cmd->subtype, rel, ATT_TABLE | 
ATT_SEQUENCE);
                        if (tab->chgPersistence)
                                ereport(ERROR,
                                                
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
@@ -4675,7 +4676,7 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
                        pass = AT_PASS_MISC;
                        break;
                case AT_SetUnLogged:    /* SET UNLOGGED */
-                       ATSimplePermissions(cmd->subtype, rel, ATT_TABLE);
+                       ATSimplePermissions(cmd->subtype, rel, ATT_TABLE | 
ATT_SEQUENCE);
                        if (tab->chgPersistence)
                                ereport(ERROR,
                                                
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
@@ -5425,7 +5426,7 @@ ATRewriteTables(AlterTableStmt *parsetree, List **wqueue, 
LOCKMODE lockmode,
                 * and assigns a new relfilenode, we automatically create or 
drop an
                 * init fork for the relation as appropriate.
                 */
-               if (tab->rewrite > 0)
+               if (tab->rewrite > 0 && tab->relkind != RELKIND_SEQUENCE)
                {
                        /* Build a temporary relation and copy data */
                        Relation        OldHeap;
@@ -5546,6 +5547,11 @@ ATRewriteTables(AlterTableStmt *parsetree, List 
**wqueue, LOCKMODE lockmode,
 
                        InvokeObjectPostAlterHook(RelationRelationId, 
tab->relid, 0);
                }
+               else if (tab->rewrite > 0 && tab->relkind == RELKIND_SEQUENCE)
+               {
+                       if (tab->chgPersistence)
+                               SequenceChangePersistence(tab->relid, 
tab->newrelpersistence);
+               }
                else
                {
                        /*
@@ -5564,6 +5570,23 @@ ATRewriteTables(AlterTableStmt *parsetree, List 
**wqueue, LOCKMODE lockmode,
                        if (tab->newTableSpace)
                                ATExecSetTableSpace(tab->relid, 
tab->newTableSpace, lockmode);
                }
+
+               /*
+                * Also change persistence of owned sequences, so that it 
matches the
+                * table persistence.
+                */
+               if (tab->chgPersistence)
+               {
+                       List       *seqlist = getOwnedSequences(tab->relid);
+                       ListCell   *lc;
+
+                       foreach(lc, seqlist)
+                       {
+                               Oid         seq_relid = lfirst_oid(lc);
+
+                               SequenceChangePersistence(seq_relid, 
tab->newrelpersistence);
+                       }
+               }
        }
 
        /*
@@ -6224,6 +6247,9 @@ ATSimplePermissions(AlterTableType cmdtype, Relation rel, 
int allowed_targets)
                case RELKIND_FOREIGN_TABLE:
                        actual_target = ATT_FOREIGN_TABLE;
                        break;
+               case RELKIND_SEQUENCE:
+                       actual_target = ATT_SEQUENCE;
+                       break;
                default:
                        actual_target = 0;
                        break;
diff --git a/src/backend/parser/parse_utilcmd.c 
b/src/backend/parser/parse_utilcmd.c
index cd946c7692..2826559d09 100644
--- a/src/backend/parser/parse_utilcmd.c
+++ b/src/backend/parser/parse_utilcmd.c
@@ -445,6 +445,7 @@ generateSerialExtraStmts(CreateStmtContext *cxt, ColumnDef 
*column,
        seqstmt = makeNode(CreateSeqStmt);
        seqstmt->for_identity = for_identity;
        seqstmt->sequence = makeRangeVar(snamespace, sname, -1);
+       seqstmt->sequence->relpersistence = cxt->relation->relpersistence;
        seqstmt->options = seqoptions;
 
        /*
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index 535b160165..3c2201a725 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -16570,6 +16570,7 @@ dumpSequence(Archive *fout, const TableInfo *tbinfo)
        PQExpBuffer query = createPQExpBuffer();
        PQExpBuffer delqry = createPQExpBuffer();
        char       *qseqname;
+       TableInfo  *owning_tab = NULL;
 
        qseqname = pg_strdup(fmtId(tbinfo->dobj.name));
 
@@ -16678,7 +16679,7 @@ dumpSequence(Archive *fout, const TableInfo *tbinfo)
 
        if (tbinfo->is_identity_sequence)
        {
-               TableInfo  *owning_tab = findTableByOid(tbinfo->owning_tab);
+               owning_tab = findTableByOid(tbinfo->owning_tab);
 
                appendPQExpBuffer(query,
                                                  "ALTER TABLE %s ",
@@ -16696,7 +16697,9 @@ dumpSequence(Archive *fout, const TableInfo *tbinfo)
        else
        {
                appendPQExpBuffer(query,
-                                                 "CREATE SEQUENCE %s\n",
+                                                 "CREATE %sSEQUENCE %s\n",
+                                                 tbinfo->relpersistence == 
RELPERSISTENCE_UNLOGGED ?
+                                                 "UNLOGGED " : "",
                                                  fmtQualifiedDumpable(tbinfo));
 
                if (strcmp(seqtype, "bigint") != 0)
@@ -16722,7 +16725,15 @@ dumpSequence(Archive *fout, const TableInfo *tbinfo)
                                          cache, (cycled ? "\n    CYCLE" : ""));
 
        if (tbinfo->is_identity_sequence)
+       {
                appendPQExpBufferStr(query, "\n);\n");
+               if (tbinfo->relpersistence != owning_tab->relpersistence)
+                       appendPQExpBuffer(query,
+                                                         "ALTER SEQUENCE %s 
SET %s;\n",
+                                                         
fmtQualifiedDumpable(tbinfo),
+                                                         
tbinfo->relpersistence == RELPERSISTENCE_UNLOGGED ?
+                                                         "UNLOGGED" : 
"LOGGED");
+       }
        else
                appendPQExpBufferStr(query, ";\n");
 
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index 4dddf08789..73bbbe2eb4 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -1681,8 +1681,12 @@ describeOneTableDetails(const char *schemaname,
                printTableInit(&cont, &myopt, title.data, 7, numrows);
                printTableInitialized = true;
 
-               printfPQExpBuffer(&title, _("Sequence \"%s.%s\""),
-                                                 schemaname, relationname);
+               if (tableinfo.relpersistence == 'u')
+                       printfPQExpBuffer(&title, _("Unlogged sequence 
\"%s.%s\""),
+                                                         schemaname, 
relationname);
+               else
+                       printfPQExpBuffer(&title, _("Sequence \"%s.%s\""),
+                                                         schemaname, 
relationname);
 
                printTableAddHeader(&cont, gettext_noop("Type"), true, 'l');
                printTableAddHeader(&cont, gettext_noop("Start"), true, 'r');
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 3f9dfffd57..89e5f01088 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -2115,7 +2115,7 @@ psql_completion(const char *text, int start, int end)
        /* ALTER SEQUENCE <name> */
        else if (Matches("ALTER", "SEQUENCE", MatchAny))
                COMPLETE_WITH("AS", "INCREMENT", "MINVALUE", "MAXVALUE", 
"RESTART",
-                                         "NO", "CACHE", "CYCLE", "SET SCHEMA", 
"OWNED BY",
+                                         "NO", "CACHE", "CYCLE", "SET", "OWNED 
BY",
                                          "OWNER TO", "RENAME TO");
        /* ALTER SEQUENCE <name> AS */
        else if (TailMatches("ALTER", "SEQUENCE", MatchAny, "AS"))
@@ -2123,6 +2123,9 @@ psql_completion(const char *text, int start, int end)
        /* ALTER SEQUENCE <name> NO */
        else if (Matches("ALTER", "SEQUENCE", MatchAny, "NO"))
                COMPLETE_WITH("MINVALUE", "MAXVALUE", "CYCLE");
+       /* ALTER SEQUENCE <name> SET */
+       else if (Matches("ALTER", "SEQUENCE", MatchAny, "SET"))
+               COMPLETE_WITH("SCHEMA", "LOGGED", "UNLOGGED");
        /* ALTER SERVER <name> */
        else if (Matches("ALTER", "SERVER", MatchAny))
                COMPLETE_WITH("VERSION", "OPTIONS", "OWNER TO", "RENAME TO");
diff --git a/src/include/commands/sequence.h b/src/include/commands/sequence.h
index 5bab90db8e..f2381982d5 100644
--- a/src/include/commands/sequence.h
+++ b/src/include/commands/sequence.h
@@ -58,6 +58,7 @@ extern List *sequence_options(Oid relid);
 
 extern ObjectAddress DefineSequence(ParseState *pstate, CreateSeqStmt *stmt);
 extern ObjectAddress AlterSequence(ParseState *pstate, AlterSeqStmt *stmt);
+extern void SequenceChangePersistence(Oid relid, char newrelpersistence);
 extern void DeleteSequenceTuple(Oid relid);
 extern void ResetSequence(Oid seq_relid);
 extern void SetSequence(Oid seq_relid, bool transactional, int64 last_value, 
int64 log_cnt, bool is_called);
diff --git a/src/test/recovery/t/014_unlogged_reinit.pl 
b/src/test/recovery/t/014_unlogged_reinit.pl
index f3199fbd2e..0dca3f69fe 100644
--- a/src/test/recovery/t/014_unlogged_reinit.pl
+++ b/src/test/recovery/t/014_unlogged_reinit.pl
@@ -18,16 +18,27 @@
 $node->start;
 my $pgdata = $node->data_dir;
 
-# Create an unlogged table to test that forks other than init are not
-# copied.
+# Create an unlogged table and an unlogged sequence to test that forks
+# other than init are not copied.
 $node->safe_psql('postgres', 'CREATE UNLOGGED TABLE base_unlogged (id int)');
+$node->safe_psql('postgres', 'CREATE UNLOGGED SEQUENCE seq_unlogged');
 
 my $baseUnloggedPath = $node->safe_psql('postgres',
        q{select pg_relation_filepath('base_unlogged')});
+my $seqUnloggedPath = $node->safe_psql('postgres',
+       q{select pg_relation_filepath('seq_unlogged')});
 
 # Test that main and init forks exist.
-ok(-f "$pgdata/${baseUnloggedPath}_init", 'init fork in base exists');
-ok(-f "$pgdata/$baseUnloggedPath",        'main fork in base exists');
+ok(-f "$pgdata/${baseUnloggedPath}_init", 'table init fork exists');
+ok(-f "$pgdata/$baseUnloggedPath",        'table main fork exists');
+ok(-f "$pgdata/${seqUnloggedPath}_init",  'sequence init fork exists');
+ok(-f "$pgdata/$seqUnloggedPath",         'sequence main fork exists');
+
+# Test the sequence
+is($node->safe_psql('postgres', "SELECT nextval('seq_unlogged')"),
+       1, 'sequence nextval');
+is($node->safe_psql('postgres', "SELECT nextval('seq_unlogged')"),
+       2, 'sequence nextval again');
 
 # Create an unlogged table in a tablespace.
 
@@ -44,6 +55,19 @@
 ok(-f "$pgdata/${ts1UnloggedPath}_init", 'init fork in tablespace exists');
 ok(-f "$pgdata/$ts1UnloggedPath",        'main fork in tablespace exists');
 
+# Create more unlogged sequences for testing.
+$node->safe_psql('postgres', 'CREATE UNLOGGED SEQUENCE seq_unlogged2');
+# This rewrites the sequence relation in AlterSequence().
+$node->safe_psql('postgres', 'ALTER SEQUENCE seq_unlogged2 INCREMENT 2');
+$node->safe_psql('postgres', "SELECT nextval('seq_unlogged2')");
+
+$node->safe_psql('postgres',
+       'CREATE UNLOGGED TABLE tab_seq_unlogged3 (a int GENERATED ALWAYS AS 
IDENTITY)'
+);
+# This rewrites the sequence relation in ResetSequence().
+$node->safe_psql('postgres', 'TRUNCATE tab_seq_unlogged3 RESTART IDENTITY');
+$node->safe_psql('postgres', 'INSERT INTO tab_seq_unlogged3 DEFAULT VALUES');
+
 # Crash the postmaster.
 $node->stop('immediate');
 
@@ -54,6 +78,8 @@
 # Remove main fork to test that it is recopied from init.
 unlink("$pgdata/${baseUnloggedPath}")
   or BAIL_OUT("could not remove \"${baseUnloggedPath}\": $!");
+unlink("$pgdata/${seqUnloggedPath}")
+  or BAIL_OUT("could not remove \"${seqUnloggedPath}\": $!");
 
 # the same for the tablespace
 append_to_file("$pgdata/${ts1UnloggedPath}_vm",  'TEST_VM');
@@ -64,13 +90,25 @@
 $node->start;
 
 # check unlogged table in base
-ok(-f "$pgdata/${baseUnloggedPath}_init", 'init fork in base still exists');
-ok(-f "$pgdata/$baseUnloggedPath", 'main fork in base recreated at startup');
+ok( -f "$pgdata/${baseUnloggedPath}_init",
+       'table init fork in base still exists');
+ok(-f "$pgdata/$baseUnloggedPath",
+       'table main fork in base recreated at startup');
 ok(!-f "$pgdata/${baseUnloggedPath}_vm",
        'vm fork in base removed at startup');
 ok( !-f "$pgdata/${baseUnloggedPath}_fsm",
        'fsm fork in base removed at startup');
 
+# check unlogged sequence
+ok(-f "$pgdata/${seqUnloggedPath}_init", 'sequence init fork still exists');
+ok(-f "$pgdata/$seqUnloggedPath", 'sequence main fork recreated at startup');
+
+# Test the sequence after restart
+is($node->safe_psql('postgres', "SELECT nextval('seq_unlogged')"),
+       1, 'sequence nextval after restart');
+is($node->safe_psql('postgres', "SELECT nextval('seq_unlogged')"),
+       2, 'sequence nextval after restart again');
+
 # check unlogged table in tablespace
 ok( -f "$pgdata/${ts1UnloggedPath}_init",
        'init fork still exists in tablespace');
@@ -81,4 +119,15 @@
 ok( !-f "$pgdata/${ts1UnloggedPath}_fsm",
        'fsm fork in tablespace removed at startup');
 
+# Test other sequences
+is($node->safe_psql('postgres', "SELECT nextval('seq_unlogged2')"),
+       1, 'altered sequence nextval after restart');
+is($node->safe_psql('postgres', "SELECT nextval('seq_unlogged2')"),
+       3, 'altered sequence nextval after restart again');
+
+$node->safe_psql('postgres',
+       "INSERT INTO tab_seq_unlogged3 VALUES (DEFAULT), (DEFAULT)");
+is($node->safe_psql('postgres', "SELECT * FROM tab_seq_unlogged3"),
+       "1\n2", 'reset sequence nextval after restart');
+
 done_testing();
diff --git a/src/test/regress/expected/alter_table.out 
b/src/test/regress/expected/alter_table.out
index 07473dd660..5ede56d9b5 100644
--- a/src/test/regress/expected/alter_table.out
+++ b/src/test/regress/expected/alter_table.out
@@ -3461,7 +3461,7 @@ ORDER BY relname;
  unlogged1             | r       | u
  unlogged1 toast index | i       | u
  unlogged1 toast table | t       | u
- unlogged1_f1_seq      | S       | p
+ unlogged1_f1_seq      | S       | u
  unlogged1_pkey        | i       | u
 (5 rows)
 
@@ -3528,7 +3528,7 @@ ORDER BY relname;
  logged1             | r       | u
  logged1 toast index | i       | u
  logged1 toast table | t       | u
- logged1_f1_seq      | S       | p
+ logged1_f1_seq      | S       | u
  logged1_pkey        | i       | u
 (5 rows)
 
diff --git a/src/test/regress/expected/sequence.out 
b/src/test/regress/expected/sequence.out
index 71c2b0f1df..7cb2f7cc02 100644
--- a/src/test/regress/expected/sequence.out
+++ b/src/test/regress/expected/sequence.out
@@ -2,8 +2,6 @@
 -- CREATE SEQUENCE
 --
 -- various error cases
-CREATE UNLOGGED SEQUENCE sequence_testx;
-ERROR:  unlogged sequences are not supported
 CREATE SEQUENCE sequence_testx INCREMENT BY 0;
 ERROR:  INCREMENT must not be zero
 CREATE SEQUENCE sequence_testx INCREMENT BY -1 MINVALUE 20;
@@ -600,6 +598,24 @@ DROP SEQUENCE seq2;
 -- should fail
 SELECT lastval();
 ERROR:  lastval is not yet defined in this session
+-- unlogged sequences
+-- (more tests in src/test/recovery/)
+CREATE UNLOGGED SEQUENCE sequence_test_unlogged;
+ALTER SEQUENCE sequence_test_unlogged SET LOGGED;
+\d sequence_test_unlogged
+                   Sequence "public.sequence_test_unlogged"
+  Type  | Start | Minimum |       Maximum       | Increment | Cycles? | Cache 
+--------+-------+---------+---------------------+-----------+---------+-------
+ bigint |     1 |       1 | 9223372036854775807 |         1 | no      |     1
+
+ALTER SEQUENCE sequence_test_unlogged SET UNLOGGED;
+\d sequence_test_unlogged
+              Unlogged sequence "public.sequence_test_unlogged"
+  Type  | Start | Minimum |       Maximum       | Increment | Cycles? | Cache 
+--------+-------+---------+---------------------+-----------+---------+-------
+ bigint |     1 |       1 | 9223372036854775807 |         1 | no      |     1
+
+DROP SEQUENCE sequence_test_unlogged;
 -- Test sequences in read-only transactions
 CREATE TEMPORARY SEQUENCE sequence_test_temp1;
 START TRANSACTION READ ONLY;
diff --git a/src/test/regress/sql/sequence.sql 
b/src/test/regress/sql/sequence.sql
index 7928ee23ee..674f5f1f66 100644
--- a/src/test/regress/sql/sequence.sql
+++ b/src/test/regress/sql/sequence.sql
@@ -3,7 +3,6 @@
 --
 
 -- various error cases
-CREATE UNLOGGED SEQUENCE sequence_testx;
 CREATE SEQUENCE sequence_testx INCREMENT BY 0;
 CREATE SEQUENCE sequence_testx INCREMENT BY -1 MINVALUE 20;
 CREATE SEQUENCE sequence_testx INCREMENT BY 1 MAXVALUE -20;
@@ -272,6 +271,15 @@ CREATE SEQUENCE seq2;
 -- should fail
 SELECT lastval();
 
+-- unlogged sequences
+-- (more tests in src/test/recovery/)
+CREATE UNLOGGED SEQUENCE sequence_test_unlogged;
+ALTER SEQUENCE sequence_test_unlogged SET LOGGED;
+\d sequence_test_unlogged
+ALTER SEQUENCE sequence_test_unlogged SET UNLOGGED;
+\d sequence_test_unlogged
+DROP SEQUENCE sequence_test_unlogged;
+
 -- Test sequences in read-only transactions
 CREATE TEMPORARY SEQUENCE sequence_test_temp1;
 START TRANSACTION READ ONLY;

base-commit: 0af504733c6e9198067705822e7527dc4e60b4f6
-- 
2.35.1

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