Fix. Pages read via SQL don't have checksum, so calculate it at the backup side. It's an arguable decision, but at least now we are able to test other possible issues.

Author: alubennikova

src/data.c

@@ -233,7 +233,8 @@ backup_data_page(pgFile *file, XLogRecPtr prev_backup_start_lsn,
 
 	int					try_again = 100;
 	bool				page_is_valid = false;
-	
+	BlockNumber absolute_blknum = file->segno * RELSEG_SIZE + blknum;
+
 	/*
 	 * Read the page and verify its header and checksum.
 	 * Under high write load it's possible that we've read partly
@@ -263,22 +264,26 @@ backup_data_page(pgFile *file, XLogRecPtr prev_backup_start_lsn,
 		(backup_mode == BACKUP_MODE_DIFF_PTRACK))
 	{
 		size_t page_size = 0;
+		PageHeader phdr = (PageHeader) page;
+
 		free(page);
 		page = NULL;
 
-		page = (Page) pg_ptrack_get_block(file->tblspcOid, file->relOid, blknum, &page_size);
+		page = (Page) pg_ptrack_get_block(file->tblspcOid, file->relOid, absolute_blknum, &page_size);
 
 		if (page == NULL)
 		{
 			elog(WARNING, "File %s, block %u, file was truncated",
-					file->path, blknum);
+					file->path, absolute_blknum);
 			return;
 		}
 
 		if (page_size != BLCKSZ)
 			elog(ERROR, "File: %s, block %u, expected block size %lu,"
 					  "but read %d, try again",
-					   file->path, blknum, page_size, BLCKSZ);
+					   file->path, absolute_blknum, page_size, BLCKSZ);
+
+		((PageHeader) page)->pd_checksum = pg_checksum_page(page, absolute_blknum);
 	}