Subject: [PATCH 3/5] Add default_toast_compression GUC

From: Dilip Kumar <[email-masked]>
Date: Wed, 10 Mar 2021 14:05:05 +0530

Justin Pryzby and Dilip Kumar
---
 src/backend/access/common/toast_compression.c | 46 +++++++++++++++++++
 src/backend/access/common/tupdesc.c           |  2 +-
 src/backend/bootstrap/bootstrap.c             |  2 +-
 src/backend/commands/tablecmds.c              |  8 ++--
 src/backend/utils/misc/guc.c                  | 12 +++++
 src/backend/utils/misc/postgresql.conf.sample |  1 +
 src/include/access/toast_compression.h        | 22 ++++++++-
 src/test/regress/expected/compression.out     | 16 +++++++
 src/test/regress/expected/compression_1.out   | 19 ++++++++
 src/test/regress/sql/compression.sql          |  8 ++++
 10 files changed, 128 insertions(+), 8 deletions(-)

diff --git a/src/backend/access/common/toast_compression.c b/src/backend/access/common/toast_compression.c
index 3463b42438..e33f92687c 100644
--- a/src/backend/access/common/toast_compression.c
+++ b/src/backend/access/common/toast_compression.c
@@ -55,6 +55,9 @@ const CompressionRoutine toast_compression[] =
 	}
 };
 
+/* Compile-time default */
+char	*default_toast_compression = DEFAULT_TOAST_COMPRESSION;
+
 /*
  * pglz_cmcompress - compression routine for pglz compression method
  *
@@ -306,3 +309,46 @@ GetCompressionRoutines(char method)
 {
 	return &toast_compression[CompressionMethodToId(method)];
 }
+
+/* check_hook: validate new default_toast_compression */
+bool
+check_default_toast_compression(char **newval, void **extra, GucSource source)
+{
+	if (**newval == '\0')
+	{
+		GUC_check_errdetail("%s cannot be empty.",
+							"default_toast_compression");
+		return false;
+	}
+
+	if (strlen(*newval) >= NAMEDATALEN)
+	{
+		GUC_check_errdetail("%s is too long (maximum %d characters).",
+							"default_toast_compression", NAMEDATALEN - 1);
+		return false;
+	}
+
+	if (!CompressionMethodIsValid(CompressionNameToMethod(*newval)))
+	{
+		/*
+		 * When source == PGC_S_TEST, don't throw a hard error for a
+		 * nonexistent compression method, only a NOTICE. See comments in
+		 * guc.h.
+		 */
+		if (source == PGC_S_TEST)
+		{
+			ereport(NOTICE,
+					(errcode(ERRCODE_UNDEFINED_OBJECT),
+						errmsg("compression method \"%s\" does not exist",
+							*newval)));
+		}
+		else
+		{
+			GUC_check_errdetail("Compression method \"%s\" does not exist.",
+								*newval);
+			return false;
+		}
+	}
+
+	return true;
+}
diff --git a/src/backend/access/common/tupdesc.c b/src/backend/access/common/tupdesc.c
index 503d64df38..a4b34ec570 100644
--- a/src/backend/access/common/tupdesc.c
+++ b/src/backend/access/common/tupdesc.c
@@ -668,7 +668,7 @@ TupleDescInitEntry(TupleDesc desc,
 	att->attcollation = typeForm->typcollation;
 
 	if (IsStorageCompressible(typeForm->typstorage))
-		att->attcompression = DefaultCompressionMethod;
+		att->attcompression = GetDefaultToastCompression();
 	else
 		att->attcompression = InvalidCompressionMethod;
 
diff --git a/src/backend/bootstrap/bootstrap.c b/src/backend/bootstrap/bootstrap.c
index 45e1cfa56c..def0ad1dcf 100644
--- a/src/backend/bootstrap/bootstrap.c
+++ b/src/backend/bootstrap/bootstrap.c
@@ -733,7 +733,7 @@ DefineAttr(char *name, char *type, int attnum, int nullness)
 	attrtypes[attnum]->atttypmod = -1;
 	attrtypes[attnum]->attislocal = true;
 	if (IsStorageCompressible(attrtypes[attnum]->attstorage))
-		attrtypes[attnum]->attcompression = DefaultCompressionMethod;
+		attrtypes[attnum]->attcompression = GetDefaultToastCompression();
 	else
 		attrtypes[attnum]->attcompression = InvalidCompressionMethod;
 
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index d295d85cd2..745dfe9570 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -11931,7 +11931,7 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
 		if (!IsStorageCompressible(tform->typstorage))
 			attTup->attcompression = InvalidCompressionMethod;
 		else if (!CompressionMethodIsValid(attTup->attcompression))
-			attTup->attcompression = DefaultCompressionMethod;
+			attTup->attcompression = GetDefaultToastCompression();
 	}
 	else
 		attTup->attcompression = InvalidCompressionMethod;
@@ -17745,9 +17745,9 @@ GetAttributeCompression(Form_pg_attribute att, char *compression)
 
 	/* fallback to default compression if it's not specified */
 	if (compression == NULL)
-		return DefaultCompressionMethod;
-
-	cmethod = CompressionNameToMethod(compression);
+		cmethod = GetDefaultToastCompression();
+	else
+		cmethod = CompressionNameToMethod(compression);
 
 	return cmethod;
 }
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 855076b1fd..321d2eb21e 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -30,6 +30,7 @@
 #include <unistd.h>
 
 #include "access/commit_ts.h"
+#include "access/toast_compression.h"
 #include "access/gin.h"
 #include "access/rmgr.h"
 #include "access/tableam.h"
@@ -3915,6 +3916,17 @@ static struct config_string ConfigureNamesString[] =
 		check_default_table_access_method, NULL, NULL
 	},
 
+	{
+		{"default_toast_compression", PGC_USERSET, CLIENT_CONN_STATEMENT,
+			gettext_noop("Sets the default compression for new columns."),
+			NULL,
+			GUC_IS_NAME
+		},
+		&default_toast_compression,
+		DEFAULT_TOAST_COMPRESSION,
+		check_default_toast_compression, NULL, NULL
+	},
+
 	{
 		{"default_tablespace", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Sets the default tablespace to create tables and indexes in."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index f46c2dd7a8..7d7a433dcc 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -659,6 +659,7 @@
 #temp_tablespaces = ''			# a list of tablespace names, '' uses
 					# only default tablespace
 #default_table_access_method = 'heap'
+#default_toast_compression = 'pglz'	# 'pglz' or 'lz4'
 #check_function_bodies = on
 #default_transaction_isolation = 'read committed'
 #default_transaction_read_only = off
diff --git a/src/include/access/toast_compression.h b/src/include/access/toast_compression.h
index 38800cb97a..e9d9ce5634 100644
--- a/src/include/access/toast_compression.h
+++ b/src/include/access/toast_compression.h
@@ -15,6 +15,14 @@
 
 #include "postgres.h"
 
+#include "utils/guc.h"
+
+/* default compression method if not specified. */
+#define DEFAULT_TOAST_COMPRESSION	"pglz"
+
+/* GUCs */
+extern char *default_toast_compression;
+
 /*
  * Built-in compression methods.  pg_attribute will store this in the
  * attcompression column.
@@ -36,8 +44,6 @@ typedef enum CompressionId
 	LZ4_COMPRESSION_ID = 1
 } CompressionId;
 
-/* use default compression method if it is not specified. */
-#define DefaultCompressionMethod PGLZ_COMPRESSION
 #define IsValidCompression(cm)  ((cm) != InvalidCompressionMethod)
 
 #define IsStorageCompressible(storage) ((storage) != TYPSTORAGE_PLAIN && \
@@ -67,6 +73,8 @@ typedef struct CompressionRoutine
 
 extern char CompressionNameToMethod(char *compression);
 extern const CompressionRoutine *GetCompressionRoutines(char method);
+extern bool check_default_toast_compression(char **newval, void **extra,
+											GucSource source);
 
 /*
  * CompressionMethodToId - Convert compression method to compression id.
@@ -115,5 +123,15 @@ GetCompressionMethodName(char method)
 	return GetCompressionRoutines(method)->cmname;
 }
 
+/*
+ * GetDefaultToastCompression -- get the current toast compression
+ *
+ * This exists to hide the use of the default_toast_compression GUC variable.
+ */
+static inline char
+GetDefaultToastCompression(void)
+{
+	return CompressionNameToMethod(default_toast_compression);
+}
 
 #endif							/* TOAST_COMPRESSION_H */
diff --git a/src/test/regress/expected/compression.out b/src/test/regress/expected/compression.out
index 1de3ae2646..12ab404900 100644
--- a/src/test/regress/expected/compression.out
+++ b/src/test/regress/expected/compression.out
@@ -211,6 +211,22 @@ CREATE TABLE cminh(f1 TEXT COMPRESSION lz4) INHERITS(cmdata);
 NOTICE:  merging column "f1" with inherited definition
 ERROR:  column "f1" has a compression method conflict
 DETAIL:  pglz versus lz4
+-- test default_toast_compression GUC
+SET default_toast_compression = '';
+ERROR:  invalid value for parameter "default_toast_compression": ""
+DETAIL:  default_toast_compression cannot be empty.
+SET default_toast_compression = 'I do not exist compression';
+ERROR:  invalid value for parameter "default_toast_compression": "I do not exist compression"
+DETAIL:  Compression method "I do not exist compression" does not exist.
+SET default_toast_compression = 'lz4';
+DROP TABLE cmdata2;
+CREATE TABLE cmdata2 (f1 text);
+\d+ cmdata2
+                                        Table "public.cmdata2"
+ Column | Type | Collation | Nullable | Default | Storage  | Compression | Stats target | Description 
+--------+------+-----------+----------+---------+----------+-------------+--------------+-------------
+ f1     | text |           |          |         | extended | lz4         |              | 
+
 -- check data is ok
 SELECT length(f1) FROM cmdata;
  length 
diff --git a/src/test/regress/expected/compression_1.out b/src/test/regress/expected/compression_1.out
index 2999b3bb79..cc9b913418 100644
--- a/src/test/regress/expected/compression_1.out
+++ b/src/test/regress/expected/compression_1.out
@@ -208,6 +208,25 @@ CREATE TABLE cminh(f1 TEXT COMPRESSION lz4) INHERITS(cmdata);
 NOTICE:  merging column "f1" with inherited definition
 ERROR:  column "f1" has a compression method conflict
 DETAIL:  pglz versus lz4
+-- test default_toast_compression GUC
+SET default_toast_compression = '';
+ERROR:  invalid value for parameter "default_toast_compression": ""
+DETAIL:  default_toast_compression cannot be empty.
+SET default_toast_compression = 'I do not exist compression';
+ERROR:  invalid value for parameter "default_toast_compression": "I do not exist compression"
+DETAIL:  Compression method "I do not exist compression" does not exist.
+SET default_toast_compression = 'lz4';
+ERROR:  unsupported LZ4 compression method
+DETAIL:  This functionality requires the server to be built with lz4 support.
+HINT:  You need to rebuild PostgreSQL using --with-lz4.
+DROP TABLE cmdata2;
+CREATE TABLE cmdata2 (f1 text);
+\d+ cmdata2
+                                        Table "public.cmdata2"
+ Column | Type | Collation | Nullable | Default | Storage  | Compression | Stats target | Description 
+--------+------+-----------+----------+---------+----------+-------------+--------------+-------------
+ f1     | text |           |          |         | extended | pglz        |              | 
+
 -- check data is ok
 SELECT length(f1) FROM cmdata;
  length 
diff --git a/src/test/regress/sql/compression.sql b/src/test/regress/sql/compression.sql
index ab35f3b4ae..0d5a2231d0 100644
--- a/src/test/regress/sql/compression.sql
+++ b/src/test/regress/sql/compression.sql
@@ -92,6 +92,14 @@ SELECT pg_column_compression(f1) FROM cmpart;
 CREATE TABLE cminh() INHERITS(cmdata, cmdata1);
 CREATE TABLE cminh(f1 TEXT COMPRESSION lz4) INHERITS(cmdata);
 
+-- test default_toast_compression GUC
+SET default_toast_compression = '';
+SET default_toast_compression = 'I do not exist compression';
+SET default_toast_compression = 'lz4';
+DROP TABLE cmdata2;
+CREATE TABLE cmdata2 (f1 text);
+\d+ cmdata2
+
 -- check data is ok
 SELECT length(f1) FROM cmdata;
 SELECT length(f1) FROM cmdata1;
-- 
2.17.0

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