Revert "Allow on-line enabling and disabling of data checksums"

This reverts the backend sides of commit 1fde38beaa.
I have, at least for now, left the pg_verify_checksums tool in place, as
this tool can be very valuable without the rest of the patch as well,
and since it's a read-only tool that only runs when the cluster is down
it should be a lot safer.

src/include/access/xlog.h

@@ -154,7 +154,7 @@ extern PGDLLIMPORT int wal_level;
  * of the bits make it to disk, but the checksum wouldn't match.  Also WAL-log
  * them if forced by wal_log_hints=on.
  */
-#define XLogHintBitIsNeeded() (DataChecksumsNeedWrite() || wal_log_hints)
+#define XLogHintBitIsNeeded() (DataChecksumsEnabled() || wal_log_hints)
 
 /* Do we need to WAL-log information required only for Hot Standby and logical replication? */
 #define XLogStandbyInfoActive() (wal_level >= WAL_LEVEL_REPLICA)
@@ -257,13 +257,7 @@ extern char *XLogFileNameP(TimeLineID tli, XLogSegNo segno);
 extern void UpdateControlFile(void);
 extern uint64 GetSystemIdentifier(void);
 extern char *GetMockAuthenticationNonce(void);
-extern bool DataChecksumsNeedWrite(void);
-extern bool DataChecksumsNeedVerify(void);
-extern bool DataChecksumsInProgress(void);
-extern void SetDataChecksumsInProgress(void);
-extern void SetDataChecksumsOn(void);
-extern void SetDataChecksumsOff(void);
-extern const char *show_data_checksums(void);
+extern bool DataChecksumsEnabled(void);
 extern XLogRecPtr GetFakeLSNForUnloggedRel(void);
 extern Size XLOGShmemSize(void);
 extern void XLOGShmemInit(void);

src/include/access/xlog_internal.h

@@ -25,7 +25,6 @@
 #include "lib/stringinfo.h"
 #include "pgtime.h"
 #include "storage/block.h"
-#include "storage/checksum.h"
 #include "storage/relfilenode.h"
 
 
@@ -241,12 +240,6 @@ typedef struct xl_restore_point
 	char		rp_name[MAXFNAMELEN];
 } xl_restore_point;
 
-/* Information logged when checksum level is changed */
-typedef struct xl_checksum_state
-{
-	ChecksumType new_checksumtype;
-}			xl_checksum_state;
-
 /* End of recovery mark, when we don't do an END_OF_RECOVERY checkpoint */
 typedef struct xl_end_of_recovery
 {

src/include/catalog/pg_control.h

@@ -76,7 +76,6 @@ typedef struct CheckPoint
 #define XLOG_END_OF_RECOVERY			0x90
 #define XLOG_FPI_FOR_HINT				0xA0
 #define XLOG_FPI						0xB0
-#define XLOG_CHECKSUMS					0xC0
 
 
 /*

src/include/catalog/pg_proc.dat

@@ -10169,14 +10169,6 @@
   proargnames => '{max_data_alignment,database_block_size,blocks_per_segment,wal_block_size,bytes_per_wal_segment,max_identifier_length,max_index_columns,max_toast_chunk_size,large_object_chunk_size,float4_pass_by_value,float8_pass_by_value,data_page_checksum_version}',
   prosrc => 'pg_control_init' },
 
-{ oid => '3996', descr => 'disable data checksums',
-  proname => 'pg_disable_data_checksums', provolatile => 'v',
-  prorettype => 'void', proargtypes => '', prosrc => 'disable_data_checksums' },
-{ oid => '3998', descr => 'enable data checksums',
-  proname => 'pg_enable_data_checksums', provolatile => 'v',
-  prorettype => 'void', proargtypes => 'int4 int4',
-  proargnames => '{cost_delay,cost_limit}', prosrc => 'enable_data_checksums' },
-
 # collation management functions
 { oid => '3445', descr => 'import collations from operating system',
   proname => 'pg_import_system_collations', procost => '100',

src/include/pgstat.h

@@ -710,9 +710,7 @@ typedef enum BackendType
 	B_STARTUP,
 	B_WAL_RECEIVER,
 	B_WAL_SENDER,
-	B_WAL_WRITER,
-	B_CHECKSUMHELPER_LAUNCHER,
-	B_CHECKSUMHELPER_WORKER
+	B_WAL_WRITER
 } BackendType;
 
 

src/include/postmaster/checksumhelper.h

@@ -1,31 +0,0 @@
-/*-------------------------------------------------------------------------
- *
- * checksumhelper.h
- *	  header file for checksum helper background worker
- *
- *
- * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
- * Portions Copyright (c) 1994, Regents of the University of California
- *
- * src/include/postmaster/checksumhelper.h
- *
- *-------------------------------------------------------------------------
- */
-#ifndef CHECKSUMHELPER_H
-#define CHECKSUMHELPER_H
-
-/* Shared memory */
-extern Size ChecksumHelperShmemSize(void);
-extern void ChecksumHelperShmemInit(void);
-
-/* Start the background processes for enabling checksums */
-bool		StartChecksumHelperLauncher(int cost_delay, int cost_limit);
-
-/* Shutdown the background processes, if any */
-void		ShutdownChecksumHelperIfRunning(void);
-
-/* Background worker entrypoints */
-void		ChecksumHelperLauncherMain(Datum arg);
-void		ChecksumHelperWorkerMain(Datum arg);
-
-#endif							/* CHECKSUMHELPER_H */

src/include/storage/bufpage.h

@@ -194,7 +194,6 @@ typedef PageHeaderData *PageHeader;
  */
 #define PG_PAGE_LAYOUT_VERSION		4
 #define PG_DATA_CHECKSUM_VERSION	1
-#define PG_DATA_CHECKSUM_INPROGRESS_VERSION		2
 
 /* ----------------------------------------------------------------
  *						page support macros

src/include/storage/checksum.h

@@ -15,13 +15,6 @@
 
 #include "storage/block.h"
 
-typedef enum ChecksumType
-{
-	DATA_CHECKSUMS_OFF = 0,
-	DATA_CHECKSUMS_ON,
-	DATA_CHECKSUMS_INPROGRESS
-}			ChecksumType;
-
 /*
  * Compute the checksum for a Postgres page.  The page must be aligned on a
  * 4-byte boundary.