diff -r c6b8eab5db19 -r b66ea3fc3a86 mercurial/revlogutils/constants.py
--- a/mercurial/revlogutils/constants.py	Fri Sep 07 11:18:45 2018 -0400
+++ b/mercurial/revlogutils/constants.py	Fri Sep 07 11:18:45 2018 -0400
@@ -41,3 +41,6 @@
 REVIDX_KNOWN_FLAGS = util.bitsfrom(REVIDX_FLAGS_ORDER)
 # bitmark for flags that could cause rawdata content change
 REVIDX_RAWTEXT_CHANGING_FLAGS = REVIDX_ISCENSORED | REVIDX_EXTSTORED
+
+SPARSE_REVLOG_MAX_CHAIN_LENGTH = 1000
+