Allow I/O reliability checks using 16-bit checksums

Checksums are set immediately prior to flush out of shared buffers
and checked when pages are read in again. Hint bit setting will
require full page write when block is dirtied, which causes various
infrastructure changes. Extensive comments, docs and README.

WARNING message thrown if checksum fails on non-all zeroes page;
ERROR thrown but can be disabled with ignore_checksum_failure = on.

Feature enabled by an initdb option, since transition from option off
to option on is long and complex and has not yet been implemented.
Default is not to use checksums.

Checksum used is WAL CRC-32 truncated to 16-bits.

Simon Riggs, Jeff Davis, Greg Smith
Wide input and assistance from many community members. Thank you.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index 8a65492a346..f8f06c1f38b 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -267,6 +267,8 @@ extern bool XLogNeedsFlush(XLogRecPtr RecPtr);
 extern int XLogFileInit(XLogSegNo segno, bool *use_existent, bool use_lock);
 extern int	XLogFileOpen(XLogSegNo segno);
 
+extern XLogRecPtr XLogSaveBufferForHint(Buffer buffer);
+
 extern void CheckXLogRemoved(XLogSegNo segno, TimeLineID tli);
 extern void XLogSetAsyncXactLSN(XLogRecPtr record);
 
@@ -294,6 +296,7 @@ extern char *XLogFileNameP(TimeLineID tli, XLogSegNo segno);
 
 extern void UpdateControlFile(void);
 extern uint64 GetSystemIdentifier(void);
+extern bool DataChecksumsEnabled(void);
 extern XLogRecPtr GetFakeLSNForUnloggedRel(void);
 extern Size XLOGShmemSize(void);
 extern void XLOGShmemInit(void);