1 files changed, 35 insertions, 4 deletions

diff --git a/src/backend/backup/basebackup_incremental.c b/src/backend/backup/basebackup_incremental.c
index 2970dfe6031..131598badef 100644
--- a/src/backend/backup/basebackup_incremental.c
+++ b/src/backend/backup/basebackup_incremental.c
@@ -929,6 +929,36 @@ GetFileBackupMethod(IncrementalBackupInfo *ib, const char *path,
 }
 
 /*
+ * Compute the size for a header of an incremental file containing a given
+ * number of blocks. The header is rounded to a multiple of BLCKSZ, but
+ * only if the file will store some block data.
+ */
+extern size_t
+GetIncrementalHeaderSize(unsigned num_blocks_required)
+{
+	size_t		result;
+
+	/* Make sure we're not going to overflow. */
+	Assert(num_blocks_required <= RELSEG_SIZE);
+
+	/*
+	 * Three four byte quantities (magic number, truncation block length,
+	 * block count) followed by block numbers.
+	 */
+	result = 3 * sizeof(uint32) + (sizeof(BlockNumber) * num_blocks_required);
+
+	/*
+	 * Round the header size to a multiple of BLCKSZ - when not a multiple of
+	 * BLCKSZ, add the missing fraction of a block. But do this only if the
+	 * file will store data for some blocks, otherwise keep it small.
+	 */
+	if ((num_blocks_required > 0) && (result % BLCKSZ != 0))
+		result += BLCKSZ - (result % BLCKSZ);
+
+	return result;
+}
+
+/*
  * Compute the size for an incremental file containing a given number of blocks.
  */
 extern size_t
@@ -940,11 +970,12 @@ GetIncrementalFileSize(unsigned num_blocks_required)
 	Assert(num_blocks_required <= RELSEG_SIZE);
 
 	/*
-	 * Three four byte quantities (magic number, truncation block length,
-	 * block count) followed by block numbers followed by block contents.
+	 * Header with three four byte quantities (magic number, truncation block
+	 * length, block count) followed by block numbers, rounded to a multiple
+	 * of BLCKSZ (for files with block data), followed by block contents.
 	 */
-	result = 3 * sizeof(uint32);
-	result += (BLCKSZ + sizeof(BlockNumber)) * num_blocks_required;
+	result = GetIncrementalHeaderSize(num_blocks_required);
+	result += BLCKSZ * num_blocks_required;
 
 	return result;
 }