fix decompression of BLCKSZ pages

Author: alubennikova

src/data.c

@@ -722,6 +722,7 @@ restore_data_file(const char *to_path, pgFile *file, bool allow_truncate,
 		size_t		read_len;
 		DataPage	compressed_page; /* used as read buffer */
 		DataPage	page;
+		int32		uncompressed_size = 0;
 
 		/* File didn`t changed. Nothig to copy */
 		if (file->write_size == BYTES_INVALID)
@@ -777,17 +778,23 @@ restore_data_file(const char *to_path, pgFile *file, bool allow_truncate,
 
 		Assert(header.compressed_size <= BLCKSZ);
 
+		/* read a page from file */
 		read_len = fread(compressed_page.data, 1,
 			MAXALIGN(header.compressed_size), in);
 		if (read_len != MAXALIGN(header.compressed_size))
 			elog(ERROR, "cannot read block %u of \"%s\" read %lu of %d",
 				blknum, file->path, read_len, header.compressed_size);
 
+		/*
+		 * if page size is smaller than BLCKSZ, decompress the page.
+		 * BUGFIX for versions < 2.0.23: if page size is equal to BLCKSZ.
+		 * we have to check, whether it is compressed or not using
+		 * page_may_be_compressed() function.
+		 */
 		if (header.compressed_size != BLCKSZ
 			|| page_may_be_compressed(compressed_page.data, file->compress_alg,
 									  backup_version))
 		{
-			int32		uncompressed_size = 0;
 			const char *errormsg = NULL;
 
 			uncompressed_size = do_decompress(page.data, BLCKSZ,
@@ -820,15 +827,19 @@ restore_data_file(const char *to_path, pgFile *file, bool allow_truncate,
 					 blknum, file->path, strerror(errno));
 		}
 
-		if (header.compressed_size < BLCKSZ)
+		/* if we uncompressed the page - write page.data,
+		 * if page wasn't compressed -
+		 * write what we've read - compressed_page.data
+		 */
+		if (uncompressed_size == BLCKSZ)
 		{
 			if (fwrite(page.data, 1, BLCKSZ, out) != BLCKSZ)
 				elog(ERROR, "cannot write block %u of \"%s\": %s",
 					 blknum, file->path, strerror(errno));
 		}
 		else
 		{
-			/* if page wasn't compressed, we've read full block */
+			/*  */
 			if (fwrite(compressed_page.data, 1, BLCKSZ, out) != BLCKSZ)
 				elog(ERROR, "cannot write block %u of \"%s\": %s",
 					 blknum, file->path, strerror(errno));