From 4e046281fb58b9986bc6de63ae3c6a8bb38342e5 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Fri, 14 May 2021 15:07:34 -0400 Subject: Prevent infinite insertion loops in spgdoinsert(). Formerly we just relied on operator classes that assert longValuesOK to eventually shorten the leaf value enough to fit on an index page. That fails since the introduction of INCLUDE-column support (commit 09c1c6ab4), because the INCLUDE columns might alone take up more than a page, meaning no amount of leaf-datum compaction will get the job done. At least with spgtextproc.c, that leads to an infinite loop, since spgtextproc.c won't throw an error for not being able to shorten the leaf datum anymore. To fix without breaking cases that would otherwise work, add logic to spgdoinsert() to verify that the leaf tuple size is decreasing after each "choose" step. Some opclasses might not decrease the size on every single cycle, and in any case, alignment roundoff of the tuple size could obscure small gains. Therefore, allow up to 10 cycles without additional savings before throwing an error. (Perhaps this number will need adjustment, but it seems quite generous right now.) As long as we've developed this logic, let's back-patch it. The back branches don't have INCLUDE columns to worry about, but this seems like a good defense against possible bugs in operator classes. We already know that an infinite loop here is pretty unpleasant, so having a defense seems to outweigh the risk of breaking things. (Note that spgtextproc.c is actually the only known opclass with longValuesOK support, so that this is all moot for known non-core opclasses anyway.) Per report from Dilip Kumar. Discussion: https://postgr.es/m/CAFiTN-uxP_soPhVG840tRMQTBmtA_f_Y8N51G7DKYYqDh7XN-A@mail.gmail.com --- doc/src/sgml/spgist.sgml | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'doc/src') diff --git a/doc/src/sgml/spgist.sgml b/doc/src/sgml/spgist.sgml index 34ea181db71..0e3cc814f15 100644 --- a/doc/src/sgml/spgist.sgml +++ b/doc/src/sgml/spgist.sgml @@ -938,6 +938,18 @@ typedef struct spgLeafConsistentOut fails to do that, the SP-GiST core resorts to extraordinary measures described in . + + + When longValuesOK is true, it is expected + that successive levels of the SP-GiST tree will + absorb more and more information into the prefixes and node labels of + the inner tuples, making the required leaf datum smaller and smaller, + so that eventually it will fit on a page. + To prevent bugs in operator classes from causing infinite insertion + loops, the SP-GiST core will raise an error if the + leaf datum does not become any smaller within ten cycles + of choose method calls. + -- cgit v1.2.3