Hello, Sergei! On Thu, 1 Sept 2022 at 15:23, Sergei Golubchik <s...@mariadb.org> wrote:
> Hi, Nikita, > > On Aug 30, Nikita Malyavin wrote: > > revision-id: b1b38b64598 (mariadb-10.5.17-4-gb1b38b64598) > > parent(s): 3b656ac8c17 > > author: Nikita Malyavin > > committer: Nikita Malyavin > > timestamp: 2022-08-23 00:27:39 +0300 > > message: > > > > MDEV-29181 Potential corruption on FK update on a table with vcol > > index > > > > vc_templ->mysql_table concept is completely broken. This table pointer > > persists with a global access and can be overwritten by arbitrary > > thread. Like it wasn't enough, it also could become invalid after > > eviction from tc cache. > > this is a bit misleading. I agree it's completely broken, though :) > > But not "this table pointer", because, of course it persists with a > global access and can be overwritten and so on. This is by design, it's > protected by mysql_table_query_id. > The problem is that table (dict_table_t) argument of > innodb_find_table_for_vc() points to a shared data structure, not thread > local, as I believed. So vc_templ is shared too. > Well, that just wasn't the only problem:) But yes, mentioning it in the commit message is worth it, too. I will think on how to rewrite it better. > > This new solution simply does the following: > > * Sets up a referenced table list in TABLE instance (sql_base.cc) > > * Iterates through it along with dict_table_t::referenced_set > > (row_upd_check_references_constraints) > > * Passes corresponding prebuilt through a call chain to > > row_ins_foreign_check_on_constraint > > * Sets up newly created upd_node_t::prebuilt field and uses it > > accordingly is cascade update. > > Is this upd_node_t::prebuilt used anywhere? As a prebuilt, I mean. > I couldn't find it (it's a complex patch, so I couldn've missed it). > As far as I can see, it's only used to store a pointer to TABLE. > > So it seems to me than a simpler fix for this bug could be: > * remove vc_templ caching (mysql_table and mysql_table_query_id) > * store TABLE* in upd_node_t. > > Not sure about the lifetimes, so it's not necessarily simpler. prebuilt is not used in this patch, but it is used during online row logging to convert the row to [my]sql format. -- Yours truly, Nikita Malyavin
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