v15-0003-Add-support-for-PRESERVE.patch

From e21010ccc7073114816ad73e70d38960d370c110 Mon Sep 17 00:00:00 2001
From: dilipkumar <dilipbalaut@gmail.com>
Date: Mon, 7 Dec 2020 11:55:39 +0530
Subject: [PATCH v15 3/6] Add support for PRESERVE

Now the compression method can be changed without forcing a table
rewrite, by including the old method in the PRESERVE list.

Dilip Kumar based on the patches from Ildus Kurbangaliev.
Design input from Tomas Vondra and Robert Haas
Reviewed by Robert Haas, Tomas Vondra, Alexander Korotkov

Discussions:
https://www.postgresql.org/message-id/20171213151818.75a20259@postgrespro.ru
https://www.postgresql.org/message-id/CA%2BTgmoaKDW1Oi9V%3Djc9hOGyf77NbkNEABuqgHD1Cq%3D%3D1QsOcxg%40mail.gmail.com
https://www.postgresql.org/message-id/CA%2BTgmobSDVgUage9qQ5P_%3DF_9jaMkCgyKxUQGtFQU7oN4kX-AA%40mail.gmail.com
https://www.postgresql.org/message-id/20201005160355.byp74sh3ejsv7wrj%40development
https://www.postgresql.org/message-id/CAFiTN-tzTTT2oqWdRGLv1dvvS5MC1W%2BLE%2B3bqWPJUZj4GnHOJg%40mail.gmail.com
---
 doc/src/sgml/ref/alter_table.sgml          |  11 +-
 src/backend/catalog/objectaddress.c        |   1 +
 src/backend/catalog/pg_depend.c            |   7 +
 src/backend/commands/Makefile              |   1 +
 src/backend/commands/compressioncmds.c     | 231 +++++++++++++++++++++
 src/backend/commands/tablecmds.c           | 117 ++++++-----
 src/backend/executor/nodeModifyTable.c     |  10 +-
 src/backend/nodes/copyfuncs.c              |  17 +-
 src/backend/nodes/equalfuncs.c             |  15 +-
 src/backend/nodes/outfuncs.c               |  15 +-
 src/backend/parser/gram.y                  |  52 ++++-
 src/backend/parser/parse_utilcmd.c         |   2 +-
 src/bin/psql/tab-complete.c                |   7 +
 src/include/commands/defrem.h              |   7 +
 src/include/nodes/nodes.h                  |   1 +
 src/include/nodes/parsenodes.h             |  16 +-
 src/test/regress/expected/compression.out  |  37 +++-
 src/test/regress/expected/create_index.out |  56 ++---
 src/test/regress/sql/compression.sql       |   9 +
 19 files changed, 517 insertions(+), 95 deletions(-)
 create mode 100644 src/backend/commands/compressioncmds.c

diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml
index bfa5c36fb7..2fb9cfaadc 100644
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@ -54,7 +54,7 @@ ALTER TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceable>
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET ( <replaceable class="parameter">attribute_option</replaceable> = <replaceable class="parameter">value</replaceable> [, ... ] )
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> RESET ( <replaceable class="parameter">attribute_option</replaceable> [, ... ] )
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN }
-    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET COMPRESSION <replaceable class="parameter">compression_method</replaceable>
+    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET COMPRESSION <replaceable class="parameter">compression_method</replaceable> [ PRESERVE (<replaceable class="parameter">compression_preserve_list</replaceable>) | PRESERVE ALL ]
     ADD <replaceable class="parameter">table_constraint</replaceable> [ NOT VALID ]
     ADD <replaceable class="parameter">table_constraint_using_index</replaceable>
     ALTER CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
@@ -386,13 +386,18 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
 
    <varlistentry>
     <term>
-     <literal>SET COMPRESSION <replaceable class="parameter">compression_method</replaceable></literal>
+     <literal>SET COMPRESSION <replaceable class="parameter">compression_method</replaceable> [ PRESERVE (<replaceable class="parameter">compression_preserve_list</replaceable>) | PRESERVE ALL ]</literal>
     </term>
     <listitem>
      <para>
       This clause adds compression to a column. Compression method can be set
       from available built-in compression methods. The available built-in
-      methods are <literal>pglz</literal> and <literal>lz4</literal>.
+      methods are <literal>pglz</literal> and <literal>lz4</literal>. The
+      PRESERVE list contains list of compression methods used on the column and
+      determines which of them should be kept on the column. Without PRESERVE or
+      if all the previous compression methods are not preserved then the table
+      will be rewritten. If PRESERVE ALL is specified then all the previous
+      methods will be preserved and the table will not be rewritten.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/backend/catalog/objectaddress.c b/src/backend/catalog/objectaddress.c
index a5eccdffd0..636364995a 100644
--- a/src/backend/catalog/objectaddress.c
+++ b/src/backend/catalog/objectaddress.c
@@ -15,6 +15,7 @@
 
 #include "postgres.h"
 
+#include "access/compressamapi.h"
 #include "access/genam.h"
 #include "access/htup_details.h"
 #include "access/relation.h"
diff --git a/src/backend/catalog/pg_depend.c b/src/backend/catalog/pg_depend.c
index 25290c821f..b198bc9b00 100644
--- a/src/backend/catalog/pg_depend.c
+++ b/src/backend/catalog/pg_depend.c
@@ -17,6 +17,7 @@
 #include "access/genam.h"
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "catalog/pg_am.h"
 #include "catalog/dependency.h"
 #include "catalog/indexing.h"
 #include "catalog/pg_collation.h"
@@ -125,6 +126,12 @@ recordMultipleDependencies(const ObjectAddress *depender,
 				if (referenced->objectId == DEFAULT_COLLATION_OID)
 					ignore_systempin = true;
 			}
+			/*
+			 * Record the dependency on compression access method for handling
+			 * preserve.
+			 */
+			if (referenced->classId == AccessMethodRelationId)
+				ignore_systempin = true;
 		}
 		else
 			Assert(!version);
diff --git a/src/backend/commands/Makefile b/src/backend/commands/Makefile
index e8504f0ae4..a7395ad77d 100644
--- a/src/backend/commands/Makefile
+++ b/src/backend/commands/Makefile
@@ -21,6 +21,7 @@ OBJS = \
 	cluster.o \
 	collationcmds.o \
 	comment.o \
+	compressioncmds.o \
 	constraint.o \
 	conversioncmds.o \
 	copy.o \
diff --git a/src/backend/commands/compressioncmds.c b/src/backend/commands/compressioncmds.c
new file mode 100644
index 0000000000..91eb59ca17
--- /dev/null
+++ b/src/backend/commands/compressioncmds.c
@@ -0,0 +1,231 @@
+/*-------------------------------------------------------------------------
+ *
+ * compressioncmds.c
+ *	  Routines for SQL commands for attribute compression methods
+ *
+ * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/commands/compressioncmds.c
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/compressamapi.h"
+#include "access/heapam.h"
+#include "access/htup_details.h"
+#include "access/reloptions.h"
+#include "catalog/catalog.h"
+#include "catalog/dependency.h"
+#include "catalog/indexing.h"
+#include "catalog/pg_attribute.h"
+#include "catalog/pg_depend.h"
+#include "commands/defrem.h"
+#include "nodes/parsenodes.h"
+#include "utils/builtins.h"
+#include "utils/fmgroids.h"
+#include "utils/lsyscache.h"
+
+/*
+ * get list of all supported compression methods for the given attribute.
+ *
+ * If oldcmoids list is passed then it will delete the attribute dependency
+ * on the compression methods passed in the oldcmoids, otherwise it will
+ * return the list of all the compression method on which the attribute has
+ * dependency.
+ */
+static List *
+lookup_attribute_compression(Oid attrelid, AttrNumber attnum, List *oldcmoids)
+{
+	LOCKMODE	lock = AccessShareLock;
+	HeapTuple	tup;
+	Relation	rel;
+	SysScanDesc scan;
+	ScanKeyData key[3];
+	List	   *cmoids = NIL;
+
+	rel = table_open(DependRelationId, lock);
+
+	ScanKeyInit(&key[0],
+				Anum_pg_depend_classid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(RelationRelationId));
+	ScanKeyInit(&key[1],
+				Anum_pg_depend_objid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(attrelid));
+	ScanKeyInit(&key[2],
+				Anum_pg_depend_objsubid,
+				BTEqualStrategyNumber, F_INT4EQ,
+				Int32GetDatum((int32) attnum));
+
+	scan = systable_beginscan(rel, DependDependerIndexId, true,
+							  NULL, 3, key);
+
+	while (HeapTupleIsValid(tup = systable_getnext(scan)))
+	{
+		Form_pg_depend depform = (Form_pg_depend) GETSTRUCT(tup);
+
+		if (depform->refclassid == AccessMethodRelationId)
+		{
+			if (oldcmoids && list_member_oid(oldcmoids, depform->refobjid))
+				CatalogTupleDelete(rel, &tup->t_self);
+			else if (oldcmoids == NULL)
+				cmoids = list_append_unique_oid(cmoids, depform->refobjid);
+		}
+	}
+
+	systable_endscan(scan);
+	table_close(rel, lock);
+
+	return cmoids;
+}
+
+/*
+ * Remove the attribute dependency on the old compression methods given in the
+ * cmoids list.
+ */
+static void
+remove_old_dependencies(Oid attrelid, AttrNumber attnum, List *cmoids)
+{
+	lookup_attribute_compression(attrelid, attnum, cmoids);
+}
+
+/*
+ * Check whether the given compression method oid is supported by
+ * the target attribue.
+ */
+bool
+IsCompressionSupported(Form_pg_attribute att, Oid cmoid)
+{
+	List	   *cmoids = NIL;
+
+	/* Check whether it is same as the current compression oid */
+	if (cmoid == att->attcompression)
+		return true;
+
+	/* Check the oid in all preserved compresion methods */
+	cmoids = lookup_attribute_compression(att->attrelid, att->attnum, NULL);
+	if (list_member_oid(cmoids, cmoid))
+		return true;
+	else
+		return false;
+}
+
+/*
+ * Get the compression method oid based on the compression method name.  When
+ * compression is not specified returns default attribute compression.  It is
+ * possible case for CREATE TABLE and ADD COLUMN commands where COMPRESSION
+ * syntax is optional.
+ *
+ * For ALTER command, check all the supported compression methods for the
+ * attribute and if the preserve list is not passed or some of the old
+ * compression methods are not given in the preserved list then delete
+ * dependency from the old compression methods and force the table rewrite.
+ */
+Oid
+GetAttributeCompression(Form_pg_attribute att, ColumnCompression *compression,
+						bool *need_rewrite)
+{
+	Oid			cmoid;
+	char		typstorage = get_typstorage(att->atttypid);
+	ListCell   *cell;
+
+	/*
+	 * No compression for the plain/external storage, refer comments atop
+	 * attcompression parameter in pg_attribute.h
+	 */
+	if (!IsStorageCompressible(typstorage))
+	{
+		if (compression != NULL)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("column data type %s does not support compression",
+							format_type_be(att->atttypid))));
+		return InvalidOid;
+	}
+
+	/* fallback to default compression if it's not specified */
+	if (compression == NULL)
+		return DefaultCompressionOid;
+
+	cmoid = get_compression_am_oid(compression->cmname, false);
+
+	/*
+	 * Determine if the column needs rewrite or not. Rewrite conditions: SET
+	 * COMPRESSION without PRESERVE - SET COMPRESSION with PRESERVE but not
+	 * with full list of previous access methods.
+	 */
+	if (need_rewrite != NULL)
+	{
+		List	   *previous_cmoids = NIL;
+
+		*need_rewrite = false;
+
+		/* If we have preserved all then rewrite is not required */
+		if (compression->preserve_all)
+			return cmoid;
+
+		previous_cmoids =
+			lookup_attribute_compression(att->attrelid, att->attnum, NULL);
+
+		if (compression->preserve != NIL)
+		{
+			foreach(cell, compression->preserve)
+			{
+				char   *cmname_p = strVal(lfirst(cell));
+				Oid		cmoid_p = get_compression_am_oid(cmname_p, false);
+
+				if (!list_member_oid(previous_cmoids, cmoid_p))
+					ereport(ERROR,
+							(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+							 errmsg("\"%s\" compression access method cannot be preserved", cmname_p),
+							 errhint("use \"pg_column_compression\" function for list of compression methods")));
+
+				/*
+				 * Remove from previous list, also protect from multiple
+				 * mentions of one access method in PRESERVE list
+				 */
+				previous_cmoids = list_delete_oid(previous_cmoids, cmoid_p);
+			}
+		}
+
+		/* delete the current cmoid from the list */
+		previous_cmoids = list_delete_oid(previous_cmoids, cmoid);
+
+		/*
+		 * If the list of previous Oids is not empty after deletions then
+		 * we need to rewrite tuples in the table.
+		 */
+		if (list_length(previous_cmoids) != 0)
+		{
+			remove_old_dependencies(att->attrelid, att->attnum,
+									previous_cmoids);
+			*need_rewrite = true;
+		}
+
+		/* Cleanup */
+		list_free(previous_cmoids);
+	}
+
+	return cmoid;
+}
+
+/*
+ * Construct ColumnCompression node from the compression method oid.
+ */
+ColumnCompression *
+MakeColumnCompression(Oid attcompression)
+{
+	ColumnCompression *node;
+
+	if (!OidIsValid(attcompression))
+		return NULL;
+
+	node = makeNode(ColumnCompression);
+	node->cmname = get_am_name(attcompression);
+
+	return node;
+}
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 7f619d1d59..91a341fc3e 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -391,6 +391,7 @@ static bool check_for_column_name_collision(Relation rel, const char *colname,
 											bool if_not_exists);
 static void add_column_datatype_dependency(Oid relid, int32 attnum, Oid typid);
 static void add_column_collation_dependency(Oid relid, int32 attnum, Oid collid);
+static void add_column_compression_dependency(Oid relid, int32 attnum, Oid cmoid);
 static void ATPrepDropNotNull(Relation rel, bool recurse, bool recursing);
 static ObjectAddress ATExecDropNotNull(Relation rel, const char *colName, LOCKMODE lockmode);
 static void ATPrepSetNotNull(List **wqueue, Relation rel,
@@ -531,7 +532,9 @@ static void ATExecEnableRowSecurity(Relation rel);
 static void ATExecDisableRowSecurity(Relation rel);
 static void ATExecForceNoForceRowSecurity(Relation rel, bool force_rls);
 static ObjectAddress ATExecSetCompression(AlteredTableInfo *tab, Relation rel,
-					 const char *column, Node *newValue, LOCKMODE lockmode);
+										  const char *column,
+										  ColumnCompression *compression,
+										  LOCKMODE lockmode);
 
 static void index_copy_data(Relation rel, RelFileNode newrnode);
 static const char *storage_name(char c);
@@ -563,7 +566,6 @@ static void refuseDupeIndexAttach(Relation parentIdx, Relation partIdx,
 static List *GetParentedForeignKeyRefs(Relation partition);
 static void ATDetachCheckNoForeignKeyRefs(Relation partition);
 static void ATExecAlterCollationRefreshVersion(Relation rel, List *coll);
-static Oid GetAttributeCompression(Form_pg_attribute att, char *compression);
 
 /* ----------------------------------------------------------------
  *		DefineRelation
@@ -588,6 +590,7 @@ ObjectAddress
 DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId,
 			   ObjectAddress *typaddress, const char *queryString)
 {
+	int			i;
 	char		relname[NAMEDATALEN];
 	Oid			namespaceId;
 	Oid			relationId;
@@ -866,7 +869,7 @@ DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId,
 			relkind == RELKIND_PARTITIONED_TABLE ||
 			relkind == RELKIND_MATVIEW)
 			attr->attcompression =
-				GetAttributeCompression(attr, colDef->compression);
+				GetAttributeCompression(attr, colDef->compression, NULL);
 		else
 			attr->attcompression = InvalidOid;
 	}
@@ -936,6 +939,20 @@ DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId,
 	 */
 	rel = relation_open(relationId, AccessExclusiveLock);
 
+	/*
+	 * Specify relation Oid in attribute compression tuples, and create
+	 * dependencies.
+	 */
+	for (i = 0; i < (RelationGetDescr(rel))->natts; i++)
+	{
+		Form_pg_attribute attr;
+
+		attr = TupleDescAttr(RelationGetDescr(rel), i);
+		if (OidIsValid(attr->attcompression))
+			add_column_compression_dependency(attr->attrelid, attr->attnum,
+											  attr->attcompression);
+	}
+
 	/*
 	 * Now add any newly specified column default and generation expressions
 	 * to the new relation.  These are passed to us in the form of raw
@@ -2414,16 +2431,17 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
 				/* Copy/check compression parameter */
 				if (OidIsValid(attribute->attcompression))
 				{
-					char *compression = get_am_name(attribute->attcompression);
+					ColumnCompression *compression =
+						MakeColumnCompression(attribute->attcompression);
 
 					if (!def->compression)
 						def->compression = compression;
-					else if (strcmp(def->compression, compression))
+					else if (strcmp(def->compression->cmname, compression->cmname))
 						ereport(ERROR,
 								(errcode(ERRCODE_DATATYPE_MISMATCH),
 								 errmsg("column \"%s\" has a compression method conflict",
 										attributeName),
-								 errdetail("%s versus %s", def->compression, compression)));
+								 errdetail("%s versus %s", def->compression->cmname, compression->cmname)));
 				}
 
 				def->inhcount++;
@@ -2460,7 +2478,8 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
 				def->collOid = attribute->attcollation;
 				def->constraints = NIL;
 				def->location = -1;
-				def->compression = get_am_name(attribute->attcompression);
+				def->compression = MakeColumnCompression(
+											attribute->attcompression);
 				inhSchema = lappend(inhSchema, def);
 				newattmap->attnums[parent_attno - 1] = ++child_attno;
 			}
@@ -2711,12 +2730,12 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
 					def->compression = newdef->compression;
 				else if (newdef->compression)
 				{
-					if (strcmp(def->compression, newdef->compression))
+					if (strcmp(def->compression->cmname, newdef->compression->cmname))
 						ereport(ERROR,
 								(errcode(ERRCODE_DATATYPE_MISMATCH),
 								 errmsg("column \"%s\" has a compression method conflict",
 										attributeName),
-								 errdetail("%s versus %s", def->compression, newdef->compression)));
+								 errdetail("%s versus %s", def->compression->cmname, newdef->compression->cmname)));
 				}
 
 				/* Mark the column as locally defined */
@@ -4801,7 +4820,8 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab, Relation rel,
 			ATExecAlterCollationRefreshVersion(rel, cmd->object);
 			break;
 		case AT_SetCompression:
-			address = ATExecSetCompression(tab, rel, cmd->name, cmd->def,
+			address = ATExecSetCompression(tab, rel, cmd->name,
+										   (ColumnCompression *) cmd->def,
 										   lockmode);
 			break;
 		default:				/* oops */
@@ -6295,7 +6315,8 @@ ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
 	if (rel->rd_rel->relkind == RELKIND_RELATION ||
 		rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
 		attribute.attcompression = GetAttributeCompression(&attribute,
-														   colDef->compression);
+														   colDef->compression,
+														   NULL);
 	else
 		attribute.attcompression = InvalidOid;
 
@@ -6470,6 +6491,7 @@ ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
 	 */
 	add_column_datatype_dependency(myrelid, newattnum, attribute.atttypid);
 	add_column_collation_dependency(myrelid, newattnum, attribute.attcollation);
+	add_column_compression_dependency(myrelid, newattnum, attribute.attcompression);
 
 	/*
 	 * Propagate to children as appropriate.  Unlike most other ALTER
@@ -6617,6 +6639,28 @@ add_column_collation_dependency(Oid relid, int32 attnum, Oid collid)
 	}
 }
 
+/*
+ * Install a dependency for compression on its column.
+ *
+ * This is used to determine connection between column and builtin
+ * compression in ALTER SET COMPRESSION command.
+ *
+ * If dependency is already there the whole thing is skipped.
+ */
+static void
+add_column_compression_dependency(Oid relid, int32 attnum, Oid cmoid)
+{
+	ObjectAddress acref,
+		attref;
+
+	Assert(relid > 0 && attnum > 0);
+
+	ObjectAddressSet(acref, AccessMethodRelationId, cmoid);
+	ObjectAddressSubSet(attref, RelationRelationId, relid, attnum);
+
+	recordMultipleDependencies(&attref, &acref, 1, DEPENDENCY_NORMAL, true);
+}
+
 /*
  * ALTER TABLE ALTER COLUMN DROP NOT NULL
  */
@@ -11752,7 +11796,8 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
 			  foundDep->refobjid == attTup->attcollation) &&
 			!(foundDep->refclassid == RelationRelationId &&
 			  foundDep->refobjid == RelationGetRelid(rel) &&
-			  foundDep->refobjsubid != 0)
+			  foundDep->refobjsubid != 0) &&
+			  foundDep->refclassid != AccessMethodRelationId
 			)
 			elog(ERROR, "found unexpected dependency for column: %s",
 				 getObjectDescription(&foundObject, false));
@@ -11867,6 +11912,11 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
 	add_column_datatype_dependency(RelationGetRelid(rel), attnum, targettype);
 	add_column_collation_dependency(RelationGetRelid(rel), attnum, targetcollid);
 
+	/* Create dependency for new attribute compression */
+	if (OidIsValid(attTup->attcompression))
+		add_column_compression_dependency(RelationGetRelid(rel), attnum,
+										  attTup->attcompression);
+
 	/*
 	 * Drop any pg_statistic entry for the column, since it's now wrong type
 	 */
@@ -15045,24 +15095,21 @@ static ObjectAddress
 ATExecSetCompression(AlteredTableInfo *tab,
 					 Relation rel,
 					 const char *column,
-					 Node *newValue,
+					 ColumnCompression *compression,
 					 LOCKMODE lockmode)
 {
 	Relation	attrel;
 	HeapTuple	tuple;
 	Form_pg_attribute atttableform;
 	AttrNumber	attnum;
-	char	   *compression;
 	char		typstorage;
 	Oid			cmoid;
+	bool		need_rewrite;
 	Datum		values[Natts_pg_attribute];
 	bool		nulls[Natts_pg_attribute];
 	bool		replace[Natts_pg_attribute];
 	ObjectAddress address;
 
-	Assert(IsA(newValue, String));
-	compression = strVal(newValue);
-
 	attrel = table_open(AttributeRelationId, RowExclusiveLock);
 
 	tuple = SearchSysCacheAttName(RelationGetRelid(rel), column);
@@ -15095,11 +15142,16 @@ ATExecSetCompression(AlteredTableInfo *tab,
 	memset(replace, false, sizeof(replace));
 
 	/* Get the attribute compression method. */
-	cmoid = GetAttributeCompression(atttableform, compression);
+	cmoid = GetAttributeCompression(atttableform, compression, &need_rewrite);
 
 	if (atttableform->attcompression != cmoid)
+		add_column_compression_dependency(atttableform->attrelid,
+										  atttableform->attnum, cmoid);
+	if (need_rewrite)
 		tab->rewrite |= AT_REWRITE_ALTER_COMPRESSION;
 
+	atttableform->attcompression = cmoid;
+
 	atttableform->attcompression = cmoid;
 	CatalogTupleUpdate(attrel, &tuple->t_self, tuple);
 
@@ -17824,32 +17876,3 @@ ATExecAlterCollationRefreshVersion(Relation rel, List *coll)
 	index_update_collation_versions(rel->rd_id, get_collation_oid(coll, false));
 	CacheInvalidateRelcache(rel);
 }
-
-/*
- * Get compression method Oid for the attribute.
- */
-static Oid
-GetAttributeCompression(Form_pg_attribute att, char *compression)
-{
-	char		typstorage = get_typstorage(att->atttypid);
-
-	/*
-	 * No compression for the plain/external storage, refer comments atop
-	 * attcompression parameter in pg_attribute.h
-	 */
-	if (!IsStorageCompressible(typstorage))
-	{
-		if (compression != NULL)
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("column data type %s does not support compression",
-							format_type_be(att->atttypid))));
-		return InvalidOid;
-	}
-
-	/* fallback to default compression if it's not specified */
-	if (compression == NULL)
-		return DefaultCompressionOid;
-
-	return get_compression_am_oid(compression, false);
-}
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index 3e62668ffc..8f952f29f7 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -45,6 +45,7 @@
 #include "access/toast_internals.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
+#include "commands/defrem.h"
 #include "commands/trigger.h"
 #include "executor/execPartition.h"
 #include "executor/executor.h"
@@ -1933,6 +1934,7 @@ CompareCompressionMethodAndDecompress(TupleTableSlot *slot,
 	int			natts = slot->tts_tupleDescriptor->natts;
 	bool		isnull = false;
 	bool		decompressed_any = false;
+	Oid			cmoid = InvalidOid;
 	TupleDesc	tupleDesc = slot->tts_tupleDescriptor;
 
 	if (natts == 0)
@@ -1963,10 +1965,12 @@ CompareCompressionMethodAndDecompress(TupleTableSlot *slot,
 
 			/*
 			 * Get the compression method stored in the toast header and
-			 * compare with the compression method of the target.
+			 * compare with the compression method of the target attribute.  If
+			 * the target compression method is not same then we need to
+			 * decompress it.
 			 */
-			if (targetTupDesc->attrs[i].attcompression !=
-				CompressionIdToOid(TOAST_COMPRESS_METHOD(new_value)))
+			cmoid = CompressionIdToOid(TOAST_COMPRESS_METHOD(new_value));
+			if (!IsCompressionSupported(&targetTupDesc->attrs[i], cmoid))
 			{
 				new_value = detoast_attr(new_value);
 				slot->tts_values[attnum - 1] = PointerGetDatum(new_value);
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index ffb8e1a58c..2ac6d61320 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -2931,7 +2931,7 @@ _copyColumnDef(const ColumnDef *from)
 
 	COPY_STRING_FIELD(colname);
 	COPY_NODE_FIELD(typeName);
-	COPY_STRING_FIELD(compression);
+	COPY_NODE_FIELD(compression);
 	COPY_SCALAR_FIELD(inhcount);
 	COPY_SCALAR_FIELD(is_local);
 	COPY_SCALAR_FIELD(is_not_null);
@@ -2951,6 +2951,18 @@ _copyColumnDef(const ColumnDef *from)
 	return newnode;
 }
 
+static ColumnCompression *
+_copyColumnCompression(const ColumnCompression *from)
+{
+	ColumnCompression *newnode = makeNode(ColumnCompression);
+
+	COPY_STRING_FIELD(cmname);
+	COPY_SCALAR_FIELD(preserve_all);
+	COPY_NODE_FIELD(preserve);
+
+	return newnode;
+}
+
 static Constraint *
 _copyConstraint(const Constraint *from)
 {
@@ -5622,6 +5634,9 @@ copyObjectImpl(const void *from)
 		case T_ColumnDef:
 			retval = _copyColumnDef(from);
 			break;
+		case T_ColumnCompression:
+			retval = _copyColumnCompression(from);
+			break;
 		case T_Constraint:
 			retval = _copyConstraint(from);
 			break;
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index cf86bdd428..51dee9e12f 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -2585,7 +2585,7 @@ _equalColumnDef(const ColumnDef *a, const ColumnDef *b)
 {
 	COMPARE_STRING_FIELD(colname);
 	COMPARE_NODE_FIELD(typeName);
-	COMPARE_STRING_FIELD(compression);
+	COMPARE_NODE_FIELD(compression);
 	COMPARE_SCALAR_FIELD(inhcount);
 	COMPARE_SCALAR_FIELD(is_local);
 	COMPARE_SCALAR_FIELD(is_not_null);
@@ -2605,6 +2605,16 @@ _equalColumnDef(const ColumnDef *a, const ColumnDef *b)
 	return true;
 }
 
+static bool
+_equalColumnCompression(const ColumnCompression *a, const ColumnCompression *b)
+{
+	COMPARE_STRING_FIELD(cmname);
+	COMPARE_SCALAR_FIELD(preserve_all);
+	COMPARE_NODE_FIELD(preserve);
+
+	return true;
+}
+
 static bool
 _equalConstraint(const Constraint *a, const Constraint *b)
 {
@@ -3677,6 +3687,9 @@ equal(const void *a, const void *b)
 		case T_ColumnDef:
 			retval = _equalColumnDef(a, b);
 			break;
+		case T_ColumnCompression:
+			retval = _equalColumnCompression(a, b);
+			break;
 		case T_Constraint:
 			retval = _equalConstraint(a, b);
 			break;
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index d2709df744..f458acae6d 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -2852,7 +2852,7 @@ _outColumnDef(StringInfo str, const ColumnDef *node)
 
 	WRITE_STRING_FIELD(colname);
 	WRITE_NODE_FIELD(typeName);
-	WRITE_STRING_FIELD(compression);
+	WRITE_NODE_FIELD(compression);
 	WRITE_INT_FIELD(inhcount);
 	WRITE_BOOL_FIELD(is_local);
 	WRITE_BOOL_FIELD(is_not_null);
@@ -2870,6 +2870,16 @@ _outColumnDef(StringInfo str, const ColumnDef *node)
 	WRITE_LOCATION_FIELD(location);
 }
 
+static void
+_outColumnCompression(StringInfo str, const ColumnCompression *node)
+{
+	WRITE_NODE_TYPE("COLUMNCOMPRESSION");
+
+	WRITE_STRING_FIELD(cmname);
+	WRITE_BOOL_FIELD(preserve_all);
+	WRITE_NODE_FIELD(preserve);
+}
+
 static void
 _outTypeName(StringInfo str, const TypeName *node)
 {
@@ -4214,6 +4224,9 @@ outNode(StringInfo str, const void *obj)
 			case T_ColumnDef:
 				_outColumnDef(str, obj);
 				break;
+			case T_ColumnCompression:
+				_outColumnCompression(str, obj);
+				break;
 			case T_TypeName:
 				_outTypeName(str, obj);
 				break;
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 9683062216..22bd0e87a3 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -593,7 +593,9 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <list>		hash_partbound
 %type <defelt>		hash_partbound_elem
 
-%type <str>	optColumnCompression
+%type <node>	optColumnCompression alterColumnCompression
+%type <str>		compressionClause
+%type <list>	optCompressionPreserve
 
 /*
  * Non-keyword token types.  These are hard-wired into the "flex" lexer.
@@ -2258,12 +2260,12 @@ alter_table_cmd:
 					$$ = (Node *)n;
 				}
 			/* ALTER TABLE <name> ALTER [COLUMN] <colname> SET (COMPRESSION <cm>) */
-			| ALTER opt_column ColId SET optColumnCompression
+			| ALTER opt_column ColId SET alterColumnCompression
 				{
 					AlterTableCmd *n = makeNode(AlterTableCmd);
 					n->subtype = AT_SetCompression;
 					n->name = $3;
-					n->def = (Node *) makeString($5);;
+					n->def = $5;
 					$$ = (Node *)n;
 				}
 			/* ALTER TABLE <name> DROP [COLUMN] IF EXISTS <colname> [RESTRICT|CASCADE] */
@@ -3386,7 +3388,7 @@ columnDef:	ColId Typename optColumnCompression create_generic_options ColQualLis
 					ColumnDef *n = makeNode(ColumnDef);
 					n->colname = $1;
 					n->typeName = $2;
-					n->compression = $3;
+					n->compression = (ColumnCompression *) $3;
 					n->inhcount = 0;
 					n->is_local = true;
 					n->is_not_null = false;
@@ -3441,13 +3443,43 @@ columnOptions:	ColId ColQualList
 				}
 		;
 
+optCompressionPreserve:
+			PRESERVE '(' name_list ')' { $$ = $3; }
+			| /*EMPTY*/ { $$ = NULL; }
+		;
+
+compressionClause:
+			COMPRESSION name { $$ = pstrdup($2); }
+		;
+
 optColumnCompression:
-					COMPRESSION name
-					{
-						$$ = $2;
-					}
-					| /*EMPTY*/	{ $$ = NULL; }
-				;
+			compressionClause
+				{
+					ColumnCompression *n = makeNode(ColumnCompression);
+					n->cmname = $1;
+					n->preserve = NIL;
+					$$ = (Node *) n;
+				}
+			| /*EMPTY*/	{ $$ = NULL; }
+		;
+
+alterColumnCompression:
+			compressionClause optCompressionPreserve
+				{
+					ColumnCompression *n = makeNode(ColumnCompression);
+					n->cmname = $1;
+					n->preserve = (List *) $2;
+					$$ = (Node *) n;
+				}
+			|	compressionClause PRESERVE ALL
+				{
+					ColumnCompression *n = makeNode(ColumnCompression);
+					n->cmname = $1;
+					n->preserve_all = true;
+					n->preserve = NIL;
+					$$ = (Node *) n;
+				}
+		;
 
 ColQualList:
 			ColQualList ColConstraint				{ $$ = lappend($1, $2); }
diff --git a/src/backend/parser/parse_utilcmd.c b/src/backend/parser/parse_utilcmd.c
index e5184933b7..4bbbf6370a 100644
--- a/src/backend/parser/parse_utilcmd.c
+++ b/src/backend/parser/parse_utilcmd.c
@@ -1086,7 +1086,7 @@ transformTableLikeClause(CreateStmtContext *cxt, TableLikeClause *table_like_cla
 		/* Likewise, copy compression if requested */
 		if (table_like_clause->options & CREATE_TABLE_LIKE_COMPRESSION
 			&& OidIsValid(attribute->attcompression))
-			def->compression = get_am_name(attribute->attcompression);
+			def->compression = MakeColumnCompression(attribute->attcompression);
 		else
 			def->compression = NULL;
 
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 1da16ebc0a..8178a5124b 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -2098,6 +2098,13 @@ psql_completion(const char *text, int start, int end)
 	else if (Matches("ALTER", "TABLE", MatchAny, "ALTER", "COLUMN", MatchAny, "SET", "(") ||
 			 Matches("ALTER", "TABLE", MatchAny, "ALTER", MatchAny, "SET", "("))
 		COMPLETE_WITH("n_distinct", "n_distinct_inherited");
+	/* ALTER TABLE ALTER [COLUMN] <foo> SET COMPRESSION */
+	else if (Matches("ALTER", "TABLE", MatchAny, "ALTER", "COLUMN", MatchAny, "SET", "COMPRESSION", MatchAny) ||
+			 Matches("ALTER", "TABLE", MatchAny, "ALTER", MatchAny, "SET", "COMPRESSION", MatchAny))
+		COMPLETE_WITH("PRESERVE");
+	else if (Matches("ALTER", "TABLE", MatchAny, "ALTER", "COLUMN", MatchAny, "SET", "COMPRESSION", MatchAny, "PRESERVE") ||
+			 Matches("ALTER", "TABLE", MatchAny, "ALTER", MatchAny, "SET", "COMPRESSION", MatchAny, "PRESERVE"))
+		COMPLETE_WITH("( ", "ALL");
 	/* ALTER TABLE ALTER [COLUMN] <foo> SET STORAGE */
 	else if (Matches("ALTER", "TABLE", MatchAny, "ALTER", "COLUMN", MatchAny, "SET", "STORAGE") ||
 			 Matches("ALTER", "TABLE", MatchAny, "ALTER", MatchAny, "SET", "STORAGE"))
diff --git a/src/include/commands/defrem.h b/src/include/commands/defrem.h
index 2d76a85336..d1880dfc5e 100644
--- a/src/include/commands/defrem.h
+++ b/src/include/commands/defrem.h
@@ -147,6 +147,13 @@ extern Oid	get_compression_am_oid(const char *amname, bool missing_ok);
 extern Oid	get_am_oid(const char *amname, bool missing_ok);
 extern char *get_am_name(Oid amOid);
 
+/* commands/compressioncmds.c */
+extern Oid GetAttributeCompression(Form_pg_attribute att,
+								   ColumnCompression *compression,
+								   bool *need_rewrite);
+extern ColumnCompression *MakeColumnCompression(Oid atttcompression);
+extern bool IsCompressionSupported(Form_pg_attribute att, Oid cmoid);
+
 /* support routines in commands/define.c */
 
 extern char *defGetString(DefElem *def);
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index c8d1f20b3b..885ff5ec5c 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -478,6 +478,7 @@ typedef enum NodeTag
 	T_PartitionBoundSpec,
 	T_PartitionRangeDatum,
 	T_PartitionCmd,
+	T_ColumnCompression,
 	T_VacuumRelation,
 
 	/*
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index af79aa6534..c8135debbb 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -623,6 +623,20 @@ typedef struct RangeTableSample
 	int			location;		/* method name location, or -1 if unknown */
 } RangeTableSample;
 
+/*
+ * ColumnCompression - compression parameters for some attribute
+ *
+ * This represents compression information defined using clause:
+ * .. COMPRESSION <compression method> PRESERVE <compression methods>
+ */
+typedef struct ColumnCompression
+{
+	NodeTag		type;
+	char	   *cmname;
+	bool		preserve_all;
+	List	   *preserve;
+} ColumnCompression;
+
 /*
  * ColumnDef - column definition (used in various creates)
  *
@@ -646,7 +660,7 @@ typedef struct ColumnDef
 	NodeTag		type;
 	char	   *colname;		/* name of column */
 	TypeName   *typeName;		/* type of column */
-	char	   *compression;	/* compression method for column */
+	ColumnCompression *compression;	/* column compression */
 	int			inhcount;		/* number of times column is inherited */
 	bool		is_local;		/* column has local (non-inherited) def'n */
 	bool		is_not_null;	/* NOT NULL constraint specified? */
diff --git a/src/test/regress/expected/compression.out b/src/test/regress/expected/compression.out
index fbbb6bf9bc..457e8bc4be 100644
--- a/src/test/regress/expected/compression.out
+++ b/src/test/regress/expected/compression.out
@@ -192,12 +192,47 @@ SELECT pg_column_compression(f1) FROM cmpart;
  lz4
 (2 rows)
 
+-- preserve old compression method
+ALTER TABLE cmdata ALTER COLUMN f1 SET COMPRESSION pglz PRESERVE (lz4);
+INSERT INTO cmdata VALUES (repeat('1234567890',1004));
+\d+ cmdata
+                                        Table "public.cmdata"
+ Column | Type | Collation | Nullable | Default | Storage  | Compression | Stats target | Description 
+--------+------+-----------+----------+---------+----------+-------------+--------------+-------------
+ f1     | text |           |          |         | extended | pglz        |              | 
+Indexes:
+    "idx" btree (f1)
+
+SELECT pg_column_compression(f1) FROM cmdata;
+ pg_column_compression 
+-----------------------
+ lz4
+ pglz
+(2 rows)
+
+\d+ cmdata
+                                        Table "public.cmdata"
+ Column | Type | Collation | Nullable | Default | Storage  | Compression | Stats target | Description 
+--------+------+-----------+----------+---------+----------+-------------+--------------+-------------
+ f1     | text |           |          |         | extended | pglz        |              | 
+Indexes:
+    "idx" btree (f1)
+
+ALTER TABLE cmdata ALTER COLUMN f1 SET COMPRESSION lz4 PRESERVE ALL;
+SELECT pg_column_compression(f1) FROM cmdata;
+ pg_column_compression 
+-----------------------
+ lz4
+ pglz
+(2 rows)
+
 -- check data is ok
 SELECT length(f1) FROM cmdata;
  length 
 --------
   10000
-(1 row)
+  10040
+(2 rows)
 
 SELECT length(f1) FROM cmdata1;
  length 
diff --git a/src/test/regress/expected/create_index.out b/src/test/regress/expected/create_index.out
index fc6afab58a..d8300bdcdd 100644
--- a/src/test/regress/expected/create_index.out
+++ b/src/test/regress/expected/create_index.out
@@ -2066,19 +2066,21 @@ WHERE classid = 'pg_class'::regclass AND
 	    'concur_reindex_ind4'::regclass,
 	    'concur_reindex_matview'::regclass)
   ORDER BY 1, 2;
-                   obj                    |                           objref                           | deptype 
-------------------------------------------+------------------------------------------------------------+---------
- index concur_reindex_ind1                | constraint concur_reindex_ind1 on table concur_reindex_tab | i
- index concur_reindex_ind2                | collation "default"                                        | n
- index concur_reindex_ind2                | column c2 of table concur_reindex_tab                      | a
- index concur_reindex_ind3                | column c1 of table concur_reindex_tab                      | a
- index concur_reindex_ind3                | table concur_reindex_tab                                   | a
- index concur_reindex_ind4                | collation "default"                                        | n
- index concur_reindex_ind4                | column c1 of table concur_reindex_tab                      | a
- index concur_reindex_ind4                | column c2 of table concur_reindex_tab                      | a
- materialized view concur_reindex_matview | schema public                                              | n
- table concur_reindex_tab                 | schema public                                              | n
-(10 rows)
+                          obj                          |                           objref                           | deptype 
+-------------------------------------------------------+------------------------------------------------------------+---------
+ column c2 of materialized view concur_reindex_matview | access method pglz                                         | n
+ column c2 of table concur_reindex_tab                 | access method pglz                                         | n
+ index concur_reindex_ind1                             | constraint concur_reindex_ind1 on table concur_reindex_tab | i
+ index concur_reindex_ind2                             | collation "default"                                        | n
+ index concur_reindex_ind2                             | column c2 of table concur_reindex_tab                      | a
+ index concur_reindex_ind3                             | column c1 of table concur_reindex_tab                      | a
+ index concur_reindex_ind3                             | table concur_reindex_tab                                   | a
+ index concur_reindex_ind4                             | collation "default"                                        | n
+ index concur_reindex_ind4                             | column c1 of table concur_reindex_tab                      | a
+ index concur_reindex_ind4                             | column c2 of table concur_reindex_tab                      | a
+ materialized view concur_reindex_matview              | schema public                                              | n
+ table concur_reindex_tab                              | schema public                                              | n
+(12 rows)
 
 REINDEX INDEX CONCURRENTLY concur_reindex_ind1;
 REINDEX TABLE CONCURRENTLY concur_reindex_tab;
@@ -2095,19 +2097,21 @@ WHERE classid = 'pg_class'::regclass AND
 	    'concur_reindex_ind4'::regclass,
 	    'concur_reindex_matview'::regclass)
   ORDER BY 1, 2;
-                   obj                    |                           objref                           | deptype 
-------------------------------------------+------------------------------------------------------------+---------
- index concur_reindex_ind1                | constraint concur_reindex_ind1 on table concur_reindex_tab | i
- index concur_reindex_ind2                | collation "default"                                        | n
- index concur_reindex_ind2                | column c2 of table concur_reindex_tab                      | a
- index concur_reindex_ind3                | column c1 of table concur_reindex_tab                      | a
- index concur_reindex_ind3                | table concur_reindex_tab                                   | a
- index concur_reindex_ind4                | collation "default"                                        | n
- index concur_reindex_ind4                | column c1 of table concur_reindex_tab                      | a
- index concur_reindex_ind4                | column c2 of table concur_reindex_tab                      | a
- materialized view concur_reindex_matview | schema public                                              | n
- table concur_reindex_tab                 | schema public                                              | n
-(10 rows)
+                          obj                          |                           objref                           | deptype 
+-------------------------------------------------------+------------------------------------------------------------+---------
+ column c2 of materialized view concur_reindex_matview | access method pglz                                         | n
+ column c2 of table concur_reindex_tab                 | access method pglz                                         | n
+ index concur_reindex_ind1                             | constraint concur_reindex_ind1 on table concur_reindex_tab | i
+ index concur_reindex_ind2                             | collation "default"                                        | n
+ index concur_reindex_ind2                             | column c2 of table concur_reindex_tab                      | a
+ index concur_reindex_ind3                             | column c1 of table concur_reindex_tab                      | a
+ index concur_reindex_ind3                             | table concur_reindex_tab                                   | a
+ index concur_reindex_ind4                             | collation "default"                                        | n
+ index concur_reindex_ind4                             | column c1 of table concur_reindex_tab                      | a
+ index concur_reindex_ind4                             | column c2 of table concur_reindex_tab                      | a
+ materialized view concur_reindex_matview              | schema public                                              | n
+ table concur_reindex_tab                              | schema public                                              | n
+(12 rows)
 
 -- Check that comments are preserved
 CREATE TABLE testcomment (i int);
diff --git a/src/test/regress/sql/compression.sql b/src/test/regress/sql/compression.sql
index f889630d62..46da711c12 100644
--- a/src/test/regress/sql/compression.sql
+++ b/src/test/regress/sql/compression.sql
@@ -82,6 +82,15 @@ ALTER TABLE cmpart1 ALTER COLUMN f1 SET COMPRESSION pglz;
 ALTER TABLE cmpart2 ALTER COLUMN f1 SET COMPRESSION lz4;
 SELECT pg_column_compression(f1) FROM cmpart;
 
+-- preserve old compression method
+ALTER TABLE cmdata ALTER COLUMN f1 SET COMPRESSION pglz PRESERVE (lz4);
+INSERT INTO cmdata VALUES (repeat('1234567890',1004));
+\d+ cmdata
+SELECT pg_column_compression(f1) FROM cmdata;
+\d+ cmdata
+ALTER TABLE cmdata ALTER COLUMN f1 SET COMPRESSION lz4 PRESERVE ALL;
+SELECT pg_column_compression(f1) FROM cmdata;
+
 -- check data is ok
 SELECT length(f1) FROM cmdata;
 SELECT length(f1) FROM cmdata1;
-- 
2.23.0