Fix bug with page compression

Author: knizhnik

src/data.c

@@ -368,7 +368,7 @@ compress_and_backup_page(pgFile *file, BlockNumber blknum,
 	BackupPageHeader header;
 	size_t		write_buffer_size = sizeof(header);
 	char		write_buffer[BLCKSZ+sizeof(header)];
-	char		compressed_page[BLCKSZ];
+	char		compressed_page[BLCKSZ*2]; /* compressed page may require more space than uncompressed */
 
 	if(page_state == SkipCurrentPage)
 		return;
@@ -395,7 +395,7 @@ compress_and_backup_page(pgFile *file, BlockNumber blknum,
 		Assert (header.compressed_size <= BLCKSZ);
 
 		/* The page was successfully compressed. */
-		if (header.compressed_size > 0)
+		if (header.compressed_size > 0 && header.compressed_size < BLCKSZ)
 		{
 			memcpy(write_buffer, &header, sizeof(header));
 			memcpy(write_buffer + sizeof(header),