UUID index bug #6916

generall · 2025-07-21T21:44:24Z

MmapHashMap had a problem with Entry alightment, in case if key value was u128. It required 16bit alightment, but
storage assumed, apparently, that nothing can need more than 8 bit alignment.

This PR introduces 2 unit tests + fix.
Fix is another alignment block inside MmapHashmap. If Required alignment is <8, there are no change and format exactly same as before. If required alignment >8, we put extra empty bytes before bucket offsets, so that
(new_alignment + buckets) % ALIGNMENT = 0.

Compatibility: luckily (thanks to @xzfc) bucket offset is stored explicitly in the header of the file.
So the same code should be able to read both: files with and without offset, even if old files were created for u128 key.

coderabbitai · 2025-07-21T23:15:47Z

📝 Walkthrough

"""

Walkthrough

The changes span three main areas. In lib/collection/src/collection/mmr/lazy_matrix.rs, the import of VectorStorage is now conditional on debug builds, restricting its inclusion to debug-only code. In lib/common/common/src/mmap_hashmap.rs, the file layout and creation logic are updated to include explicit alignment before the buckets section, error handling for u128 key deserialization is improved, and new tests for u128 keys and values are added. In lib/segment/src/index/field_index/map_index/mod.rs, a new test is introduced to verify the handling of UUID-based payload indices, particularly focusing on the payload_blocks method.

Estimated code review effort

2 (~20 minutes)

Possibly related PRs

[mmr] compute similarities lazily #6877: Introduces the LazyMatrix struct and its use of VectorStorage in the same file where the conditional import change is made, directly connecting to the updated import logic.

Suggested reviewers

coszio
"""

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Reviewing files that changed from the base of the PR and between f31acf4 and 2f6f452.

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lib/common/common/src/mmap_hashmap.rs (8 hunks)

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lib/common/common/src/mmap_hashmap.rs

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Old files without this fix create a panic on startup, which initializes the shard as dummy

ERROR qdrant::startup: Panic occurred in file lib/common/common/src/mmap_hashmap.rs at line 473: Error reading u128 from mmap: The conversion failed because the address of the source is not a multiple of the alignment of the destination type.

Source type: &[u8]
Source address: 0x11cff0728 (a multiple of 8)
Destination type: u128
Destination alignment: 16

generall · 2025-07-22T07:13:41Z

Old files without this fix create a panic on startup, which initializes the shard as dummy

this is not a new behavior, but it is a behavior of the debug build. Previous version also paniked, now it will panic(in debug) earlier, and print error messages in production.

lib/common/common/src/mmap_hashmap.rs

xzfc · 2025-07-22T07:52:02Z

Also, not related to this particular PR, but it's better not to bake align_of into on-disk structures: align_of is platform and compiler version dependent. See https://blog.rust-lang.org/2024/03/30/i128-layout-update/.

I.e., in lib/common/common/src/mmap_hashmap.rs:

 impl Key for u128 {
-    const ALIGN: usize = align_of::<u128>();
+    const ALIGN: usize = size_of::<u128>();

* reproduce bug as unit test * reproduce in even faster unit test * fix alignment in mmap_hashmap * clippy * review fixes

generall added 3 commits July 21, 2025 23:43

reproduce bug as unit test

4b1907e

reproduce in even faster unit test

69cbb26

fix alignment in mmap_hashmap

00eb892

generall requested a review from xzfc July 21, 2025 23:12

clippy

f31acf4

generall marked this pull request as ready for review July 21, 2025 23:13

generall requested a review from coszio July 21, 2025 23:15

coszio previously approved these changes Jul 21, 2025

View reviewed changes

xzfc reviewed Jul 22, 2025

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lib/common/common/src/mmap_hashmap.rs Outdated Show resolved Hide resolved

lib/common/common/src/mmap_hashmap.rs Outdated Show resolved Hide resolved

review fixes

2f6f452

generall requested review from xzfc and coszio July 22, 2025 08:39

xzfc approved these changes Jul 22, 2025

View reviewed changes

coszio approved these changes Jul 22, 2025

View reviewed changes

generall merged commit 6fdf445 into dev Jul 22, 2025
21 of 22 checks passed

generall deleted the fix-uuid-mmap-index branch July 22, 2025 18:26

generall added a commit that referenced this pull request Jul 24, 2025

UUID index bug (#6916)

6c9e12f

* reproduce bug as unit test * reproduce in even faster unit test * fix alignment in mmap_hashmap * clippy * review fixes

eek mentioned this pull request Aug 25, 2025

Loosing (text) indexes over time. #7132

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generall commented Jul 21, 2025 •

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