Random LRU Cache Request Trace Generator

Description

Generate bounded key bursts with declared previous-burst locality probability and retain least-to-most-recent cache snapshots, hits, evictions and exact global request counts.

An operation trace pairs an ordered request stream with the state after each step. Empty operations, ties, evictions, and boundary indexes are part of the modeled contract rather than incidental display details.

Generate bounded key bursts with declared previous-burst locality probability and retain least-to-most-recent cache snapshots, hits, evictions and exact global request counts.

When to use this tool

Use this generator to create reproducible lru cache request trace cases from the supplied model or bank. Inspect the returned evidence before using cases in a test or exercise.

How to use the tool and how it works

Supply keys, capacity, eventCount, burstLength, localityProbability in the field shapes below. Set seed when you need an explicit replay.
Run the tool and correct any input error. For generated controls, distinguish a successful fixture containing an invalid case from failure to generate the fixture.
Read requests, events, hitCount, counts. Use the conventions below and keep answer-bearing fields separate when presenting an exercise.

Generate bursts of repeated keys, optionally reusing the preceding burst's key. Simulate least-recently-used replacement with recency ordered oldest to newest, moving hits to the end and evicting the front on a full-cache miss.^[1]

Input field	Meaning and units	Accepted input
keys	Keys	Required. Array of Text; maximum UTF-16 length 64.; minimum items 2; maximum items 16.
capacity	Capacity	Required. Safe integer; minimum 1; maximum 16.
eventCount	Event Count	Required. Safe integer; minimum 1; maximum 64.
burstLength	Burst Length	Required. Safe integer; minimum 1; maximum 8.
localityProbability	Locality Probability	Required. Finite number; minimum 0; maximum 1.
seed	Optional numeric seed; takes precedence over context randomness. Without either, use the fixed tool.io default seed.	Optional. Safe integer.

Output field	Interpretation	Returned shape
requests	Requests	Required. Array of Text; maximum UTF-16 length 64.; minimum items 0; maximum items 64.
events	Events	Required. Array of Object; no unknown keys.; minimum items 0; maximum items 64.
events[].key	Key	Required. Text; maximum UTF-16 length 64.
events[].hit	Hit	Required. Boolean.
events[].evicted	Evicted	Required. Text; maximum UTF-16 length 64. or Null.
events[].recency	Recency	Required. Array of Text; maximum UTF-16 length 64.; minimum items 0; maximum items 16.
hitCount	Hit Count	Required. Safe integer; minimum 0; maximum 64.
counts	Counts	Required. Array of Object; no unknown keys.; minimum items 0; maximum items 16.
counts[].key	Key	Required. Text; maximum UTF-16 length 64.
counts[].count	Requested count; the mechanics explain whether one draw expands into several returned records.	Required. Safe integer; minimum 1; maximum 64.
randomness	Replay metadata: source is seed or context; seed is the normalized 32-bit seed or null for a context source.	Required. Object; no unknown keys.
randomness.seed	Optional numeric replay seed; normalization and precedence are explained below.	Required. Safe integer. or Null.
randomness.source	Source	Required. Text; one of "context", "seed".

An explicit safe-integer seed takes precedence over injected context randomness and is normalized to an unsigned 32-bit integer. With no seed and no context source, replay uses the fixed tool.io default seed. A context source must return finite values from zero inclusive to one exclusive; its advancing state must be retained separately. randomness records the source and normalized seed, or null for context. These generators are not cryptographic random sources.

json

{
  "input": {
    "keys": [
      "a",
      "b",
      "c"
    ],
    "capacity": 2,
    "eventCount": 5,
    "burstLength": 2,
    "localityProbability": 0,
    "seed": 42
  },
  "output": {
    "requests": [
      "b",
      "b",
      "c",
      "c",
      "a"
    ],
    "events": [
      {
        "key": "b",
        "hit": false,
        "evicted": null,
        "recency": [
          "b"
        ]
      },
      {
        "key": "b",
        "hit": true,
        "evicted": null,
        "recency": [
          "b"
        ]
      },
      {
        "key": "c",
        "hit": false,
        "evicted": null,
        "recency": [
          "b",
          "c"
        ]
      },
      {
        "key": "c",
        "hit": true,
        "evicted": null,
        "recency": [
          "b",
          "c"
        ]
      },
      {
        "key": "a",
        "hit": false,
        "evicted": "b",
        "recency": [
          "c",
          "a"
        ]
      }
    ],
    "hitCount": 2,
    "counts": [
      {
        "key": "b",
        "count": 2
      },
      {
        "key": "c",
        "count": 2
      },
      {
        "key": "a",
        "count": 1
      }
    ],
    "randomness": {
      "seed": 42,
      "source": "seed"
    }
  }
}

Limitations and assumptions

A fresh key draw can equal the preceding key even when the locality branch is not taken. Counts are synthetic sequential requests, not measured cache performance, concurrency, or latency.
A replay requires the same complete input and implementation. Randomized construction does not guarantee uniform coverage of every feasible output; finite samples can repeat unless a distinct-selection rule is explicitly stated.
The field tables state structural bounds; cross-field constraints and bounded search or output budgets also apply. Unknown keys are rejected where the object contract disallows them. Input errors are distinct from null fields and deliberate invalid controls in a successful output.

Alternative or Complementary methods

For a supplied example, inspect the returned construction or delegated check directly. To evaluate a consumer, also test cases chosen for its own boundaries; a generated finite corpus does not establish exhaustive coverage.

References

Tool behavior and example: Random LRU Cache Request Trace Generator — tool.io

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