perf: O(1) readset dedup in OCC multiversion store

[bdchatham]

Summary

• UpdateReadSet in the OCC multiversion store (VersionIndexedStore) previously used a linear scan with bytes.Equal to deduplicate values per key
• Added a parallel readsetDedup index (map[string]map[string]struct{}) for O(1) dedup lookups
• The ReadSet type and all consumers (validation, SetReadset, iterators) are unchanged — only the internal dedup path is faster
• Net: +16 / -12 lines, no behavior change

Motivation

UpdateReadSet is called on every storage read in every parallel transaction. For iterator-heavy workloads (range scans over storage, e.g., DEX order books, token holder lists), the same keys are visited multiple times within a single tx, triggering the dedup check each time. The previous O(n) scan with bytes.Equal compounded across many reads. OCC is enabled by default on all Sei validators (occ-enabled = true).

Design

Rather than changing the ReadSet type (which would ripple across the codebase), we keep the existing [][]byte slice for the public interface and add a private map[string]struct{} set per key as a shadow index. Both are updated together in UpdateReadSet. The dedup check hits the map (O(1)), while validation and SetReadset continue to read from the slice.

Test plan

• All 30+ multiversion store tests pass (go test ./sei-cosmos/store/multiversion/)
• gofmt -s -l clean
• go build clean

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[github-actions]

The latest Buf updates on your PR. Results from workflow Buf / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Apr 14, 2026, 6:39 PM

[codecov]

Codecov Report

❌ Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.26%. Comparing base (9795d18) to head (9a5802d).

Files with missing lines	Patch %	Lines
sei-cosmos/store/multiversion/mvkv.go	77.77%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3245   +/-   ##
=======================================
  Coverage   59.26%   59.26%           
=======================================
  Files        2070     2070           
  Lines      169788   169791    +3     
=======================================
+ Hits       100631   100634    +3     
  Misses      60358    60358           
  Partials     8799     8799           

Flag	Coverage Δ
sei-chain-pr	91.33% <77.77%> (?)
sei-db	70.41% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
sei-cosmos/store/multiversion/mvkv.go	91.07% <77.77%> (+0.16%)	⬆️

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