Allow on-line enabling and disabling of data checksums

This makes it possible to turn checksums on in a live cluster, without
the previous need for dump/reload or logical replication (and to turn it
off).

Enabling checkusm starts a background process in the form of a
launcher/worker combination that goes through the entire database and
recalculates checksums on each and every page. Only when all pages have
been checksummed are they fully enabled in the cluster. Any failure of
the process will revert to checksums off and the process has to be
started.

This adds a new WAL record that indicates the state of checksums, so
the process works across replicated clusters.

Authors: Magnus Hagander and Daniel Gustafsson
Review: Tomas Vondra, Michael Banck, Heikki Linnakangas, Andrey Borodin

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() (DataChecksumsEnabled() || wal_log_hints)
+#define XLogHintBitIsNeeded() (DataChecksumsNeedWrite() || 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)
@@ -257,7 +257,13 @@ extern char *XLogFileNameP(TimeLineID tli, XLogSegNo segno);
 extern void UpdateControlFile(void);
 extern uint64 GetSystemIdentifier(void);
 extern char *GetMockAuthenticationNonce(void);
-extern bool DataChecksumsEnabled(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 XLogRecPtr GetFakeLSNForUnloggedRel(void);
 extern Size XLOGShmemSize(void);
 extern void XLOGShmemInit(void);

src/include/access/xlog_internal.h

@@ -25,6 +25,7 @@
 #include "lib/stringinfo.h"
 #include "pgtime.h"
 #include "storage/block.h"
+#include "storage/checksum.h"
 #include "storage/relfilenode.h"
 
 
@@ -240,6 +241,12 @@ 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/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201804051
+#define CATALOG_VERSION_NO	201804052
 
 #endif

src/include/catalog/pg_control.h

@@ -76,6 +76,7 @@ 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.h

@@ -5583,6 +5583,11 @@ DESCR("pg_controldata recovery state information as a function");
 DATA(insert OID = 3444 ( pg_control_init PGNSP PGUID 12 1 0 0 0 f f f t f v s 0 0 2249 "" "{23,23,23,23,23,23,23,23,23,16,16,23}" "{o,o,o,o,o,o,o,o,o,o,o,o}" "{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}" _null_ _null_ pg_control_init _null_ _null_ _null_ ));
 DESCR("pg_controldata init state information as a function");
 
+DATA(insert OID = 3996 ( pg_disable_data_checksums		PGNSP PGUID 12 1 0 0 0 f f f t f v s 0 0 2278 "" _null_ _null_ _null_ _null_ _null_ disable_data_checksums _null_ _null_ _null_ ));
+DESCR("disable data checksums");
+DATA(insert OID = 3998 ( pg_enable_data_checksums		PGNSP PGUID 12 1 0 0 0 f f f t f v s 2 0 2278 "23 23" _null_ _null_ "{cost_delay,cost_limit}" _null_ _null_ enable_data_checksums _null_ _null_ _null_ ));
+DESCR("enable data checksums");
+
 /* collation management functions */
 DATA(insert OID = 3445 ( pg_import_system_collations PGNSP PGUID 12 100 0 0 0 f f f t f v u 1 0 23 "4089" _null_ _null_ _null_ _null_ _null_ pg_import_system_collations _null_ _null_ _null_ ));
 DESCR("import collations from operating system");

src/include/pgstat.h

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

src/include/postmaster/checksumhelper.h

@@ -0,0 +1,31 @@
+/*-------------------------------------------------------------------------
+ *
+ * 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

@@ -194,6 +194,7 @@ 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

@@ -15,6 +15,13 @@
 
 #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.