Walkthrough

This set of changes introduces hardware counter instrumentation into the posting list subsystem. The PostingListView struct is extended to include a ConditionedCounter, which is now passed through all constructors and used to track I/O or memory access costs during chunk and remainder access, as well as decompression operations. The ValueHandler trait and its implementations are updated so that get_value receives a reference to the counter, allowing for instrumentation of variable-sized data reads. All direct accesses to chunks and remainders in the posting list view and visitor are replaced by accessor methods that increment the counter as appropriate.

Possibly related PRs

• Don't measure in-memory hw for full text indices #6309: Introduces the ConditionedCounter::never() method, which is used in this PR for hardware counter instrumentation and to replace direct PhantomData usage.
• Fix measuring in memory inverted index #6316: Also modifies lib/segment/src/index/field_index/full_text_index/mmap_inverted_index/mmap_postings.rs to integrate ConditionedCounter for hardware counter instrumentation, directly affecting how counters are passed and used in MmapPostings.
• Generalize compressed posting list #6528: Provides the foundational implementation of compressed posting lists and value handling traits, which this PR extends by adding hardware counter instrumentation and modifying construction and access patterns.

Suggested reviewers

• timvisee
• generall

Configuration used: CodeRabbit UI
Review profile: CHILL
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Learnt from: coszio
PR: qdrant/qdrant#6565
File: lib/posting_list/src/builder.rs:63-67
Timestamp: 2025-05-26T14:47:23.505Z
Learning: In the posting_list crate's PostingChunk struct, avoid adding extra fields like storing computed chunk_bits to prevent struct bloat and maintain mmap compatibility. The bit calculations from offsets are inexpensive compared to the memory and compatibility benefits of keeping the struct minimal.

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