5ae2087202 implemented a cross-page unique constraint check by loading
the right sibling to the BtreeCheckState.target variable. This is wrong,
because bt_target_page_check() shouldn't change the target page. Also,
BtreeCheckState.target shouldn't be changed alone without
BtreeCheckState.targetblock.
However, the above didn't cause any visible bugs for the following reasons.
1. We do a cross-page unique constraint check only for leaf index pages.
2. The only way target page get accessed after a cross-page unique constraint
check is loading of the lowkey.
3. The only place lowkey is used is bt_child_highkey_check(), and that applies
only to non-leafs.
The reasons above don't diminish the fact that changing BtreeCheckState.target
for a cross-page unique constraint check is wrong. This commit changes this
check to temporarily store the right sibling to the local variable.
Reported-by: Peter Geoghegan
Discussion: https://postgr.es/m/CAH2-Wzk%2B2116uOXdOViA27SHcr31WKPgmjsxXLBs_aTxAeThzg%40mail.gmail.com
Author: Pavel Borisov
The PostgreSQL contrib tree
---------------------------
This subtree contains porting tools, analysis utilities, and plug-in
features that are not part of the core PostgreSQL system, mainly
because they address a limited audience or are too experimental to be
part of the main source tree. This does not preclude their
usefulness.
User documentation for each module appears in the main SGML
documentation.
When building from the source distribution, these modules are not
built automatically, unless you build the "world" target. You can
also build and install them all by running "make all" and "make
install" in this directory; or to build and install just one selected
module, do the same in that module's subdirectory.
Some directories supply new user-defined functions, operators, or
types. To make use of one of these modules, after you have installed
the code you need to register the new SQL objects in the database
system by executing a CREATE EXTENSION command. In a fresh database,
you can simply do
CREATE EXTENSION module_name;
See the PostgreSQL documentation for more information about this
procedure.
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