Set custom sysid 12.11 #2
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balbaev
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Jun 9, 2022
Due to how pg_size_pretty(bigint) was implemented, it's possible that when given a negative number of bytes that the returning value would not match the equivalent positive return value when given the equivalent positive number of bytes. This was due to two separate issues. 1. The function used bit shifting to convert the number of bytes into larger units. The rounding performed by bit shifting is not the same as dividing. For example -3 >> 1 = -2, but -3 / 2 = -1. These two operations are only equivalent with positive numbers. 2. The half_rounded() macro rounded towards positive infinity. This meant that negative numbers rounded towards zero and positive numbers rounded away from zero. Here we fix #1 by dividing the values instead of bit shifting. We fix #2 by adjusting the half_rounded macro always to round away from zero. Additionally, adjust the pg_size_pretty(numeric) function to be more explicit that it's using division rather than bit shifting. A casual observer might have believed bit shifting was used due to a static function being named numeric_shift_right. However, that function was calculating the divisor from the number of bits and performed division. Here we make that more clear. This change is just cosmetic and does not affect the return value of the numeric version of the function. Here we also add a set of regression tests both versions of pg_size_pretty() which test the values directly before and after the function switches to the next unit. This bug was introduced in 8a1fab3. Prior to that negative values were always displayed in bytes. Author: Dean Rasheed, David Rowley Discussion: https://postgr.es/m/CAEZATCXnNW4HsmZnxhfezR5FuiGgp+mkY4AzcL5eRGO4fuadWg@mail.gmail.com Backpatch-through: 9.6, where the bug was introduced.
balbaev
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Jun 9, 2022
Due to how pg_size_pretty(bigint) was implemented, it's possible that when given a negative number of bytes that the returning value would not match the equivalent positive return value when given the equivalent positive number of bytes. This was due to two separate issues. 1. The function used bit shifting to convert the number of bytes into larger units. The rounding performed by bit shifting is not the same as dividing. For example -3 >> 1 = -2, but -3 / 2 = -1. These two operations are only equivalent with positive numbers. 2. The half_rounded() macro rounded towards positive infinity. This meant that negative numbers rounded towards zero and positive numbers rounded away from zero. Here we fix #1 by dividing the values instead of bit shifting. We fix #2 by adjusting the half_rounded macro always to round away from zero. Additionally, adjust the pg_size_pretty(numeric) function to be more explicit that it's using division rather than bit shifting. A casual observer might have believed bit shifting was used due to a static function being named numeric_shift_right. However, that function was calculating the divisor from the number of bits and performed division. Here we make that more clear. This change is just cosmetic and does not affect the return value of the numeric version of the function. Here we also add a set of regression tests both versions of pg_size_pretty() which test the values directly before and after the function switches to the next unit. This bug was introduced in 8a1fab3. Prior to that negative values were always displayed in bytes. Author: Dean Rasheed, David Rowley Discussion: https://postgr.es/m/CAEZATCXnNW4HsmZnxhfezR5FuiGgp+mkY4AzcL5eRGO4fuadWg@mail.gmail.com Backpatch-through: 9.6, where the bug was introduced.
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/[email protected]
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