feat: Make SSD cache maxEntries limit configurable

[zacw7]

== RELEASE NOTES ==

Prestissimo
* Add ``ssd-cache-max-entries`` config to limit SSD cache entries and prevent unbounded metadata memory growth (default value: 10M entries, ~500MB metadata).  :pr:`26795`

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Adds a configurable upper bound on the number of SSD cache entries and wires it through system configuration to the SSD cache setup, with a default of 10M entries (~500MB metadata).

Sequence diagram for propagating SSD cache maxEntries into SsdCache

sequenceDiagram
  participant PrestoServer
  participant SystemConfig
  participant SsdCacheConfig
  participant SsdCache

  PrestoServer->>SystemConfig: ssdCacheReadVerificationEnabled()
  SystemConfig-->>PrestoServer: bool
  PrestoServer->>SystemConfig: ssdCacheMaxEntries()
  SystemConfig-->>PrestoServer: uint64_t
  PrestoServer->>SsdCacheConfig: create cacheConfig(..., ssdCacheReadVerificationEnabled, ssdCacheMaxEntries)
  SsdCacheConfig-->>PrestoServer: cacheConfig
  PrestoServer->>SsdCache: create SsdCache(cacheConfig)

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Class diagram for new SSD cache maxEntries configuration flow

classDiagram
  class SystemConfig {
    +bool ssdCacheReadVerificationEnabled()
    +uint64_t ssdCacheMaxEntries()
  }
  class PrestoServer {
    +std::unique_ptr~velox::cache::SsdCache~ setupSsdCache()
  }
  class SsdCacheConfig {
    +SsdCacheConfig(uint64_t ssdCacheSize, uint64_t ssdCacheCheckpointSize, bool asyncCacheSsdDisableFileCow, bool ssdCacheChecksumEnabled, bool ssdCacheReadVerificationEnabled, uint64_t ssdCacheMaxEntries)
  }
  class SsdCache {
    +SsdCache(SsdCacheConfig cacheConfig)
  }

  PrestoServer --> SystemConfig : uses
  PrestoServer --> SsdCacheConfig : creates
  PrestoServer --> SsdCache : creates
  SsdCacheConfig --> SsdCache : configures

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File-Level Changes

Change	Details	Files
Introduce a new ssd-cache-max-entries system configuration property with a default of 10M entries.	Declare new config key constant kSsdCacheMaxEntries and document its semantics and default in SystemConfig Register kSsdCacheMaxEntries as a numeric property with default 10,000,000 in the SystemConfig constructor Expose a typed accessor ssdCacheMaxEntries() returning uint64_t via optionalProperty	presto-native-execution/presto_cpp/main/common/Configs.h presto-native-execution/presto_cpp/main/common/Configs.cpp
Plumb the new SSD cache max-entries limit into SSD cache initialization and document the config.	Extend PrestoServer::setupSsdCache() to pass ssdCacheMaxEntries() into the velox::cache::SsdCache configuration Update Presto C++ properties documentation to describe the new ssd-cache-max-entries configuration option and its default	presto-native-execution/presto_cpp/main/PrestoServer.cpp presto-docs/src/main/sphinx/presto_cpp/properties.rst

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[sourcery-ai]

Hey there - I've reviewed your changes - here's some feedback:

• The new ssdCacheMaxEntries config uses uint64_t, but most config numerics are signed; consider using a signed type and explicitly validating non-negative values to avoid surprising wraparound if a negative value is configured.
• The comment states that 0 means "no limit" for ssdCacheMaxEntries, but this behavior isn't visible in the changes here; ensure that the underlying SsdCache / cacheConfig actually implements this semantic so the config description matches behavior.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The new `ssdCacheMaxEntries` config uses `uint64_t`, but most config numerics are signed; consider using a signed type and explicitly validating non-negative values to avoid surprising wraparound if a negative value is configured.
- The comment states that `0` means "no limit" for `ssdCacheMaxEntries`, but this behavior isn't visible in the changes here; ensure that the underlying `SsdCache` / `cacheConfig` actually implements this semantic so the config description matches behavior.

## Individual Comments

### Comment 1
<location> `presto-docs/src/main/sphinx/presto_cpp/properties.rst:553-554` </location>
<code_context>
+* **Default value:** ``10000000``
+
+  Maximum number of entries allowed in the SSD cache. A value of 0 means no limit.
+  When the limit is reached, new entry writes will be skipped.
+
+  The default of 10 million entries keeps metadata memory usage around 500MB, as each
</code_context>

<issue_to_address>
**nitpick (typo):** Consider rephrasing "new entry writes" for clarity

You could instead say “writes of new entries” or “writes of additional entries” so it’s clearer that only writes of new entries are skipped once the limit is reached.

```suggestion
  Maximum number of entries allowed in the SSD cache. A value of 0 means no limit.
  When the limit is reached, writes of new entries will be skipped.
```
</issue_to_address>

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