Subject: [PATCH v24 03/10] Add default_toast_compression GUC

From: Justin Pryzby <[email-masked]>
Date: Fri, 29 Jan 2021 21:37:46 -0600

---
 src/backend/access/common/tupdesc.c |   2 +-
 src/backend/bootstrap/bootstrap.c   |   3 +-
 src/backend/commands/amcmds.c       | 143 +++++++++++++++++++++++++++-
 src/backend/commands/tablecmds.c    |   4 +-
 src/backend/utils/init/postinit.c   |   4 +
 src/backend/utils/misc/guc.c        |  12 +++
 src/include/access/amapi.h          |   2 +
 src/include/access/compressamapi.h  |  12 ++-
 8 files changed, 176 insertions(+), 6 deletions(-)

diff --git a/src/backend/access/common/tupdesc.c b/src/backend/access/common/tupdesc.c
index ca26fab487..7afaea000b 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 = DefaultCompressionOid;
+		att->attcompression = GetDefaultToastCompression();
 	else
 		att->attcompression = InvalidOid;
 
diff --git a/src/backend/bootstrap/bootstrap.c b/src/backend/bootstrap/bootstrap.c
index 9b451eaa71..ec3376cf8a 100644
--- a/src/backend/bootstrap/bootstrap.c
+++ b/src/backend/bootstrap/bootstrap.c
@@ -732,8 +732,9 @@ DefineAttr(char *name, char *type, int attnum, int nullness)
 	attrtypes[attnum]->attcacheoff = -1;
 	attrtypes[attnum]->atttypmod = -1;
 	attrtypes[attnum]->attislocal = true;
+
 	if (IsStorageCompressible(attrtypes[attnum]->attstorage))
-		attrtypes[attnum]->attcompression = DefaultCompressionOid;
+		attrtypes[attnum]->attcompression = GetDefaultToastCompression();
 	else
 		attrtypes[attnum]->attcompression = InvalidOid;
 
diff --git a/src/backend/commands/amcmds.c b/src/backend/commands/amcmds.c
index 3ad4a61739..1682afd2a4 100644
--- a/src/backend/commands/amcmds.c
+++ b/src/backend/commands/amcmds.c
@@ -13,8 +13,11 @@
  */
 #include "postgres.h"
 
+#include "access/amapi.h"
+#include "access/compressamapi.h"
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
 #include "catalog/indexing.h"
@@ -27,13 +30,20 @@
 #include "parser/parse_func.h"
 #include "utils/builtins.h"
 #include "utils/lsyscache.h"
+#include "utils/guc.h"
+#include "utils/inval.h"
 #include "utils/rel.h"
 #include "utils/syscache.h"
 
-
 static Oid	lookup_am_handler_func(List *handler_name, char amtype);
 static const char *get_am_type_string(char amtype);
 
+/* Compile-time default */
+char	*default_toast_compression = DEFAULT_TOAST_COMPRESSION; // maybe needs pg_dump support ?
+/* Invalid means need to lookup the text value in the catalog */
+static Oid	default_toast_compression_oid = InvalidOid;
+
+static void AccessMethodCallback(Datum arg, int cacheid, uint32 hashvalue);
 
 /*
  * CreateAccessMethod
@@ -277,3 +287,134 @@ lookup_am_handler_func(List *handler_name, char amtype)
 
 	return handlerOid;
 }
+
+/* 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 we aren't inside a transaction, or not connected to a database, we
+	 * cannot do the catalog access necessary to verify the method.  Must
+	 * accept the value on faith.
+	 */
+	if (IsTransactionState() && MyDatabaseId != InvalidOid)
+	{
+		if (!OidIsValid(get_compression_am_oid(*newval, true)))
+		{
+			/*
+			 * When source == PGC_S_TEST, don't throw a hard error for a
+			 * nonexistent table access method, only a NOTICE. See comments in
+			 * guc.h.
+			 */
+			if (source == PGC_S_TEST)
+			{
+				ereport(NOTICE,
+						(errcode(ERRCODE_UNDEFINED_OBJECT),
+						 errmsg("compression access method \"%s\" does not exist",
+								*newval)));
+			}
+			else
+			{
+				GUC_check_errdetail("Compression access method \"%s\" does not exist.",
+									*newval);
+				return false;
+			}
+		}
+	}
+
+	return true;
+}
+
+/*
+ * assign_default_toast_compression: GUC assign_hook for default_toast_compression
+ */
+void
+assign_default_toast_compression(const char *newval, void *extra)
+{
+	/*
+	 * Invalidate setting, forcing it to be looked up as needed.
+	 * This avoids trying to do database access during GUC initialization,
+	 * or outside a transaction.
+	 */
+
+	default_toast_compression = NULL;
+fprintf(stderr, "set to null\n");
+}
+
+
+/*
+ * GetDefaultToastCompression -- get the OID of the current toast compression
+ *
+ * This exists to hide and optimize the use of the default_toast_compression
+ * GUC variable.
+ */
+Oid
+GetDefaultToastCompression(void)
+{
+	/* Avoid catalog access during bootstrap, and for default compression */
+	if (strcmp(default_toast_compression, DEFAULT_TOAST_COMPRESSION) == 0)
+		return PGLZ_COMPRESSION_AM_OID;
+
+	/* Cannot call get_compression_am_oid this early */
+	// if (IsBootstrapProcessingMode())
+		// return PGLZ_COMPRESSION_AM_OID;
+	Assert(!IsBootstrapProcessingMode());
+
+	/*
+	 * If cached value isn't valid, look up the current default value, caching
+	 * the result
+	 */
+	if (!OidIsValid(default_toast_compression_oid))
+		default_toast_compression_oid =
+			get_am_type_oid(default_toast_compression, AMTYPE_COMPRESSION,
+					false);
+
+	return default_toast_compression_oid;
+}
+
+/*
+ * InitializeAccessMethods: initialize module during InitPostgres.
+ *
+ * This is called after we are up enough to be able to do catalog lookups.
+ */
+void
+InitializeAccessMethods(void)
+{
+	if (IsBootstrapProcessingMode())
+		return;
+
+	/*
+	 * In normal mode, arrange for a callback on any syscache invalidation
+	 * of pg_am rows.
+	 */
+	CacheRegisterSyscacheCallback(AMOID,
+								  AccessMethodCallback,
+								  (Datum) 0);
+	/* Force cached default access method to be recomputed on next use */
+	// default_toast_compression_oid = InvalidOid;
+}
+
+/*
+ * AccessMethodCallback
+ *		Syscache inval callback function
+ */
+static void
+AccessMethodCallback(Datum arg, int cacheid, uint32 hashvalue)
+{
+	/* Force look up of compression oid on next use */
+	default_toast_compression_oid = false;
+}
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index dd81d5bf4e..72ba017814 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -11925,7 +11925,7 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
 		if (!IsStorageCompressible(tform->typstorage))
 			attTup->attcompression = InvalidOid;
 		else if (!OidIsValid(attTup->attcompression))
-			attTup->attcompression = DefaultCompressionOid;
+			attTup->attcompression = GetDefaultToastCompression();
 	}
 	else
 		attTup->attcompression = InvalidOid;
@@ -17762,7 +17762,7 @@ GetAttributeCompression(Form_pg_attribute att, char *compression)
 
 	/* fallback to default compression if it's not specified */
 	if (compression == NULL)
-		return DefaultCompressionOid;
+		return GetDefaultToastCompression();
 
 	amoid = get_compression_am_oid(compression, false);
 
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index e5965bc517..6a02bbd377 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -25,6 +25,7 @@
 #include "access/session.h"
 #include "access/sysattr.h"
 #include "access/tableam.h"
+#include "access/amapi.h"
 #include "access/xact.h"
 #include "access/xlog.h"
 #include "catalog/catalog.h"
@@ -1060,6 +1061,9 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 	/* set default namespace search path */
 	InitializeSearchPath();
 
+	/* set callback for changes to pg_am */
+	InitializeAccessMethods();
+
 	/* initialize client encoding */
 	InitializeClientEncoding();
 
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index eafdb1118e..3a2b33fcd1 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/compressamapi.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, assign_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/include/access/amapi.h b/src/include/access/amapi.h
index d357ebb559..1513cafcf4 100644
--- a/src/include/access/amapi.h
+++ b/src/include/access/amapi.h
@@ -287,4 +287,6 @@ typedef struct IndexAmRoutine
 extern IndexAmRoutine *GetIndexAmRoutine(Oid amhandler);
 extern IndexAmRoutine *GetIndexAmRoutineByAmId(Oid amoid, bool noerror);
 
+void InitializeAccessMethods(void);
+
 #endif							/* AMAPI_H */
diff --git a/src/include/access/compressamapi.h b/src/include/access/compressamapi.h
index 5a8e23d926..d75a8e9df2 100644
--- a/src/include/access/compressamapi.h
+++ b/src/include/access/compressamapi.h
@@ -17,6 +17,7 @@
 
 #include "catalog/pg_am_d.h"
 #include "nodes/nodes.h"
+#include "utils/guc.h"
 
 /*
  * Built-in compression method-id.  The toast compression header will store
@@ -29,8 +30,17 @@ typedef enum CompressionId
 	LZ4_COMPRESSION_ID = 1
 } CompressionId;
 
-/* Use default compression method if it is not specified. */
+/* Default compression method if not specified. */
+#define DEFAULT_TOAST_COMPRESSION "pglz"
 #define DefaultCompressionOid	PGLZ_COMPRESSION_AM_OID
+
+/* GUC */
+extern char       *default_toast_compression;
+extern void assign_default_toast_compression(const char *newval, void *extra);
+extern bool check_default_toast_compression(char **newval, void **extra, GucSource source);
+
+extern Oid GetDefaultToastCompression(void);
+
 #define IsStorageCompressible(storage) ((storage) != TYPSTORAGE_PLAIN && \
 										(storage) != TYPSTORAGE_EXTERNAL)
 /* compression handler routines */
-- 
2.17.0

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