Hello,
I was reading GiST core codes when I found an XLogInsert()
call that can produce a corrupt WAL record.
== Summary ==
There is an execution path that produces a WAL record whose
xl_info indicates XLOG_GIST_PAGE_UPDATE while the record
actually contains a gistxlogPageSplit structure.
== Details ==
(Line numbers are for HEAD as of Wed Dec 23 19:42:15 2009 +0000.)
The problematic XLogInsert() call is on gistxlog.c, line 770:
recptr = XLogInsert(RM_GIST_ID, XLOG_GIST_PAGE_UPDATE, rdata);
where the last argument rdata has a pointer assigned either
on line 741 or on line 752.
When rdata comes from formSplitRdata() at line 741,
rdata contains a reference to a gistxlogPageSplit structure.
This is inconsistent with the second argument XLOG_GIST_PAGE_UPDATE.
== Importance ==
I think this poses possible data loss under multiple consequent crashes.
== Fix ==
I attach a simple patch (for HEAD as of the datetime above)
that, I suppose, prevents the corrupt WAL production.
I would be glad if you liked it.
Please note that the problematic execution path exists at
least in current HEAD, REL8_2_STABLE and the branches in between.
Sincerely,
--
Yoichi Hirai
Dept. of Computer Science, The University of Tokyo.
