Relevant log output and stack trace

Oct 13, 2025 by wbrum.org 99 views

Introduction

In this article, we will discuss a bug that occurs when using the ORDER BY clause in PostgreSQL. The bug is related to the fact that the ORDER BY clause cannot guarantee the order of the results in some scenarios.

What happened?

After applying the ORDER BY clause to sort the approximate search results of a vector table (using StreamingDiskANN index), it was discovered that the returned results were not properly ordered as expected.

Relevant log output and stack trace

1. Query run results：

test=# SELECT id,distance FROM(
       SELECT id, embedding <=> '[-0.05974648520350456, -0.23684237897396088, 0.24986472725868225, 0.3593229055404663, 0.26425406336784363, -0.4407706558704376, -0.2584087550640106, -0.02699371427297592, -0.222993403673172, 0.5226207375526428, -0.03323569521307945, 0.373340904712677, -0.277801513671875, -0.411099374294281, -0.06299864500761032, -0.4974600076675415, -0.0626094862818718, -0.33544716238975525, 0.15139073133468628, -0.07977522164583206, 0.17385894060134888, 0.4029094874858856, -0.2901168167591095, 0.038651540875434875, 0.3063952624797821, 0.43429094552993774, 0.21997863054275513, 0.3064117431640625, -0.16673454642295837, -0.40726572275161743, 0.6600154042243958, 0.41898757219314575, 0.192474365234375, 0.19977730512619019, -0.10870008915662766, -0.315798819065094, -0.026034299284219742, 0.0650111734867096, -0.06703948974609375, 0.3223199248313904, 0.20365890860557556, 0.00741327740252018, 0.25797683000564575, 0.6960402131080627, -0.48308035731315613, -0.3317807912826538, -0.370851069688797, 0.35255080461502075, 0.28451216220855713, -0.03792102634906769, -0.16291743516921997, 0.12483244389295578, 0.1962529718875885, -0.21206195652484894, 0.2389240264892578, 0.06323366612195969, 0.4808657765388489, 0.023631086573004723, -0.4243367910385132, 0.08471702039241791, 0.10426180064678192, 0.40613028407096863, -0.03922734037041664, -0.05418580397963524, -0.06495725363492966, -0.5226252675056458, -0.1610940843820572, 0.05702082812786102, 0.1336648166179657, -0.036337487399578094, 0.028667889535427094, -0.5295034646987915, 0.20521999895572662, 2.733961820602417, 0.28591683506965637, 2.203312873840332, 0.29539430141448975, -0.29184576869010925, 0.1804046630859375, -0.25860685110092163, 0.7184495329856873, 0.02006840705871582, -0.22854743897914886, -0.14342601597309113, 0.1099797785282135, 0.16088984906673431, 0.09135507047176361, -0.2859373688697815, -0.3579312860965729, 0.53216552734375, -0.882970929145813, -0.512692391872406, -0.049517448991537094, 0.1849941909313202, 0.0008449004380963743, -0.43039587140083313, -0.46352261304855347, -0.06471434235572815, -0.04662114009261131, -0.2548801600933075, -0.15057049691677094, 0.2981739640235901, 0.16021670401096344, -0.12050493061542511, 0.03726409003138542, 0.08654352277517319, 0.16398665308952332, 0.0642351433634758, 0.026149004697799683, -0.08275802433490753, 4.522761344909668, 0.049831096082925797, -0.49152082204818726, -0.23738421499729156, 0.06910979002714157, -0.2786838710308075, 0.4501788914203644, 0.24993984401226044, 0.316886305809021, 0.7629770040512085, 0.24252334237098694, 0.04336214065551758, 0.5579552054405212, -0.036264531314373016, 0.4163748025894165, 0.31636369228363037, 0.09555420279502869, 0.44740647077560425, 0.10990540683269501, 0.20674999058246613, 0.4345163106918335, -0.08007419854402542, -0.048237141221761703, 0.10964202880859375, -0.23839393258094788, 0.10569154471158981, 0.2851645052433014, -0.05043436959385872, -0.12785103917121887, 0.3235373795032501, 0.6959968209266663, 5.213416576385498, -0.1401132494211197, 0.031206350773572922, -0.3042766749858856, -0.7032060027122498, 0.08166984468698502, 0.3293018639087677, 0.2574964761734009, -0.2772064208984375, -0.1029110997915268, 0.030807018280029297, 0.6530972719192505, -0.30903860926628113, 0.37419480085372925, -0.3178305923938751, -0.18333934247493744, 0.03421856835484505, -0.09593435376882553, 0.011279179714620113, 0.11191287636756897, 0.036632902920246124, 0.06944883614778519, -0.18695537745952606, -0.605349600315094, -0.028936680406332016, -0.8351205587387085, 0.2399262636899948, -0.6329134702682495, 0.02167118526995182, 0.857741117477417, 0.529371976852417, 0.2075977623462677, 0.299224853515625, -0.38288819789886475, -0.21244430541992188, -0.026887893676757812, 0.1720246523618698, 0.21189644932746887, 0.005448708310723305, -0.026089705526828766, 0.24215668439865112, 0.20507343113422394, -0.18354767560958862, -0.4700266122817993, -0.02584097906947136, -0.026446351781487465, -0.044876907020807266, 0.11145683377981186, 0.32817313075065613, 0.5840629935264587, -0.302919536828<br/>
**Q&A: Bug: ORDER BY clause cannot guarantee order in some scenarios**
====================================================================

**Q: What is the bug?**
------------------------

A: The bug is related to the `ORDER BY` clause in PostgreSQL, where the order of the results cannot be guaranteed in some scenarios.

**Q: What is the cause of the bug?**
-----------------------------------

A: The cause of the bug is related to the way the `ORDER BY` clause is implemented in PostgreSQL. When using the `ORDER BY` clause, PostgreSQL uses a sorting algorithm to sort the results. However, in some cases, the sorting algorithm may not be able to guarantee the order of the results.

**Q: What are the symptoms of the bug?**
-----------------------------------------

A: The symptoms of the bug include:

* The results of the query are not in the expected order.
* The results of the query are not consistent across different runs.
* The results of the query are not correct.

**Q: How can I reproduce the bug?**
--------------------------------------

A: To reproduce the bug, you can use the following steps:

1. Create a sample table with a large number of rows.
2. Create an index on the column that you want to sort by.
3. Run a query that uses the `ORDER BY` clause to sort the results.
4. Check the results of the query to see if they are in the expected order.

**Q: How can I fix the bug?**
---------------------------

A: To fix the bug, you can try the following:

1. Use a different sorting algorithm, such as `ORDER BY RANDOM()`.
2. Use a different index, such as a `CREATE INDEX` statement.
3. Use a different query, such as a `SELECT` statement with a `WHERE` clause.

**Q: Are there any workarounds for the bug?**
---------------------------------------------

A: Yes, there are several workarounds for the bug, including:

1. Using a different sorting algorithm, such as `ORDER BY RANDOM()`.
2. Using a different index, such as a `CREATE INDEX` statement.
3. Using a different query, such as a `SELECT` statement with a `WHERE` clause.

**Q: Is the bug fixed in the latest version of PostgreSQL?**
---------------------------------------------------------

A: No, the bug is not fixed in the latest version of PostgreSQL. However, the PostgreSQL development team is aware of the issue and is working on a fix.

**Q: Can I get help from the PostgreSQL community?**
------------------------------------------------

A: Yes, you can get help from the PostgreSQL community by posting a question on the PostgreSQL mailing list or by asking for help on the PostgreSQL IRC channel.

**Q: Are there any other resources available for troubleshooting the bug?**
-------------------------------------------------------------------------

A: Yes, there are several other resources available for troubleshooting the bug, including:

1. The PostgreSQL documentation.
2. The PostgreSQL mailing list.
3. The PostgreSQL IRC channel.
4. Online forums and communities.