After calling XLogInitBufferForRedo(), the page might be all-zeros if it was
not in page cache already. btree_xlog_unlink_page initialized the page
correctly, but it called PageGetSpecialPointer before initializing it, which
would lead to a corrupt page at WAL replay, if the unlinked page is not in
page cache.
Backpatch to 9.4, the bug came with the rewrite of B-tree page deletion.
buffer = XLogInitBufferForRedo(record, 3);
page = (Page) BufferGetPage(buffer);
- pageop = (BTPageOpaque) PageGetSpecialPointer(page);
_bt_pageinit(page, BufferGetPageSize(buffer));
+ pageop = (BTPageOpaque) PageGetSpecialPointer(page);
+
pageop->btpo_flags = BTP_HALF_DEAD | BTP_LEAF;
pageop->btpo_prev = xlrec->leafleftsib;
pageop->btpo_next = xlrec->leafrightsib;