Migrate page checksum filter to C.

This filter exactly mimics the behavior of the Perl filter so is a drop-in replacement.

The filter is not integrated yet since it requires the Perl-to-C storage layer interface coming in a future commit.

src/postgres/interface.c

@@ -14,13 +14,6 @@ PostgreSQL Interface
 #include "postgres/version.h"
 #include "storage/helper.h"
 
-/***********************************************************************************************************************************
-Define default page size
-
-Page size can only be changed at compile time and is not known to be well-tested, so only the default page size is supported.
-***********************************************************************************************************************************/
-#define PG_PAGE_SIZE_DEFAULT                                        ((unsigned int)(8 * 1024))
-
 /***********************************************************************************************************************************
 Define default wal segment size
 

src/postgres/interface.h

@@ -17,6 +17,21 @@ Defines for various Postgres paths and files
 #define PG_PATH_ARCHIVE_STATUS                                      "archive_status"
 #define PG_PATH_GLOBAL                                              "global"
 
+/***********************************************************************************************************************************
+Define default page size
+
+Page size can only be changed at compile time and is not known to be well-tested, so only the default page size is supported.
+***********************************************************************************************************************************/
+#define PG_PAGE_SIZE_DEFAULT                                        ((unsigned int)(8 * 1024))
+
+/***********************************************************************************************************************************
+Define default segment size and pages per segment
+
+Segment size can only be changed at compile time and is not known to be well-tested, so only the default segment size is supported.
+***********************************************************************************************************************************/
+#define PG_SEGMENT_SIZE_DEFAULT                                     ((unsigned int)(1 * 1024 * 1024 * 1024))
+#define PG_SEGMENT_PAGE_DEFAULT                                     (PG_SEGMENT_SIZE_DEFAULT / PG_PAGE_SIZE_DEFAULT)
+
 /***********************************************************************************************************************************
 PostgreSQL Control File Info
 ***********************************************************************************************************************************/

src/postgres/pageChecksum.c

@@ -69,6 +69,7 @@ minimize register spilling. For less sophisticated compilers it might be benefic
 #include "common/debug.h"
 #include "common/error.h"
 #include "common/log.h"
+#include "postgres/interface.h"
 #include "postgres/pageChecksum.h"
 
 /***********************************************************************************************************************************
@@ -203,6 +204,20 @@ pageChecksum(const unsigned char *page, unsigned int blockNo, unsigned int pageS
     FUNCTION_TEST_RETURN((uint16_t)(checksum % 65535 + 1));
 }
 
+/***********************************************************************************************************************************
+Return the lsn for a page
+***********************************************************************************************************************************/
+uint64_t
+pageLsn(const unsigned char *page)
+{
+    FUNCTION_TEST_BEGIN();
+        FUNCTION_TEST_PARAM_P(UCHARDATA, page);
+    FUNCTION_TEST_END();
+
+    // Reduce to a uint16 with an offset of one. That avoids checksums of zero, which seems like a good idea.
+    FUNCTION_TEST_RETURN((uint64_t)((PageHeader)page)->pd_lsn.walid << 32 | ((PageHeader)page)->pd_lsn.xrecoff);
+}
+
 /***********************************************************************************************************************************
 pageChecksumTest - test if checksum is valid for a single page
 ***********************************************************************************************************************************/
@@ -225,8 +240,8 @@ pageChecksumTest(
         ((PageHeader)page)->pd_upper == 0 ||
         // LSN is after the backup started so checksum is not tested because pages may be torn
         (((PageHeader)page)->pd_lsn.walid >= ignoreWalId && ((PageHeader)page)->pd_lsn.xrecoff >= ignoreWalOffset) ||
-        // Checksum is valid
-        ((PageHeader)page)->pd_checksum == pageChecksum(page, blockNo, pageSize));
+        // Checksum is valid if a full page
+        (pageSize == PG_PAGE_SIZE_DEFAULT && ((PageHeader)page)->pd_checksum == pageChecksum(page, blockNo, pageSize)));
 }
 
 /***********************************************************************************************************************************

src/postgres/pageChecksum.h

@@ -10,6 +10,7 @@ Checksum Implementation for Data Pages
 Functions
 ***********************************************************************************************************************************/
 uint16_t pageChecksum(const unsigned char *page, unsigned int blockNo, unsigned int pageSize);
+uint64_t pageLsn(const unsigned char *page);
 bool pageChecksumTest(
     const unsigned char *page, unsigned int blockNo, unsigned int pageSize, uint32_t ignoreWalId, uint32_t ignoreWalOffset);
 bool pageChecksumBufferTest(