Set custom sysid 13.7 #3
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balbaev
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Aug 8, 2022
We've heard a couple of reports of people having trouble with multi-gigabyte-sized query-texts files. It occurred to me that on 32-bit platforms, there could be an issue with integer overflow of calculations associated with the total query text size. Address that with several changes: 1. Limit pg_stat_statements.max to INT_MAX / 2 not INT_MAX. The hashtable code will bound it to that anyway unless "long" is 64 bits. We still need overflow guards on its use, but this helps. 2. Add a check to prevent extending the query-texts file to more than MaxAllocHugeSize. If it got that big, qtext_load_file would certainly fail, so there's not much point in allowing it. Without this, we'd need to consider whether extent, query_offset, and related variables shouldn't be off_t not size_t. 3. Adjust the comparisons in need_gc_qtexts() to be done in 64-bit arithmetic on all platforms. It appears possible that under duress those multiplications could overflow 32 bits, yielding a false conclusion that we need to garbage-collect the texts file, which could lead to repeatedly garbage-collecting after every hash table insertion. Per report from Bruno da Silva. I'm not convinced that these issues fully explain his problem; there may be some other bug that's contributing to the query-texts file becoming so large in the first place. But it did get that big, so #2 is a reasonable defense, and #3 could explain the reported performance difficulties. (See also commit 8bbe4cb, which addressed some related bugs. The second Discussion: link is the thread that led up to that.) This issue is old, and is primarily a problem for old platforms, so back-patch. Discussion: https://postgr.es/m/CAB+Nuk93fL1Q9eLOCotvLP07g7RAv4vbdrkm0cVQohDVMpAb9A@mail.gmail.com Discussion: https://postgr.es/m/5601D354.5000703@BlueTreble.com
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