MDEV-21205 Assertion failure in btr_sec_min_rec_mark

In commit af5947f433e98d0447960da07856eb207dd09e01
the function btr_discard_page() is invoking btr_set_min_rec_mark()
with the wrong buf_block_t* object. node_ptr is on merge_block,
not block.

btr_discard_page(): Remove the variables merge_page, page, and
always refer to block->frame or merge_block->frame instead.
Also, limit the scope of node_ptr and avoid duplicated conditions.

btr_set_min_rec_mark(): Add a template parameter, so that the
caller can specify whether the page is supposed to have a left sibling.
Otherwise, the assertion (which was introduced in the same commit)
would fail in btr_discard_page().

1 files changed, 4 insertions, 2 deletions

diff --git a/storage/innobase/include/btr0btr.h b/storage/innobase/include/btr0btr.h
index c2d7c786bc5..e23ad166534 100644
--- a/storage/innobase/include/btr0btr.h
+++ b/storage/innobase/include/btr0btr.h
@@ -523,16 +523,18 @@ btr_insert_on_non_leaf_level_func(
 #define btr_insert_on_non_leaf_level(f,i,l,t,m)			\
 	btr_insert_on_non_leaf_level_func(f,i,l,t,__FILE__,__LINE__,m)
 
-/** Set a record as the predefined minimum record.
+/** Set a child page pointer record as the predefined minimum record.
+@tparam has_prev  whether the page is supposed to have a left sibling
 @param[in,out]  rec     leftmost record on a leftmost non-leaf page
 @param[in,out]  block   buffer pool block
 @param[in,out]  mtr     mini-transaction */
+template<bool has_prev= false>
 inline void btr_set_min_rec_mark(rec_t *rec, const buf_block_t &block,
                                  mtr_t *mtr)
 {
   ut_ad(block.frame == page_align(rec));
   ut_ad(!page_is_leaf(block.frame));
-  ut_ad(!page_has_prev(block.frame));
+  ut_ad(has_prev == page_has_prev(block.frame));
 
   rec-= page_rec_is_comp(rec) ? REC_NEW_INFO_BITS : REC_OLD_INFO_BITS;