In Apache Ignite 2, read data in native persistent storage through the usual Ignite cache API or SQL/JDBC—not by opening partition files. Ignite manages the disk copy and loads as much data into RAM as possible. This guide covers Ignite 2’s native persistence; a separate database connected through CacheStore has a different read-through behavior. Ignite 3 uses a different storage workflow, so do not apply these Ignite 2 steps to it.
Choose the right read path
| What you need | Use | Important distinction |
|---|---|---|
| Read a known key from an Ignite 2 cache using native persistence | Cache key-value API, such as get(key) |
Ignite resolves the value whether its page is currently in RAM or must be retrieved from its managed storage. |
| Filter, project, or query records in Ignite | Ignite SQL API or JDBC | Check that the cache’s SQL fields, tables, and indexes are configured for the query. |
Read through to a separate database attached with CacheStore |
Key-value get() or getAll() |
get() can invoke CacheStore.load(); getAll() can invoke loadAll(). SQL does not fetch missing rows from that external source. |
| Run SQL on records held in an external database | Preload the records into Ignite with loadCache() |
Preloading puts records in Ignite; it is not SQL querying the external database through read-through. |
| Inspect partition or index files outside normal application use | Ignite 2 Index Reader utility | Use only for offline diagnosis, not as the application’s data-access API. |
Read data from Ignite 2 native persistence
Native persistence is Ignite’s own storage system. Each server node persists the partitions assigned to it, including backups when configured. Ignite stores data pages, indexes, and metadata on disk, and loads as much data into RAM as available capacity allows. The normal cache and SQL interfaces remain the way applications access that data; they abstract whether a needed page is already resident in memory.
Read one known key
Use the cache’s key-value API, for example get(key), when you know the cache and key. First ensure the Ignite node is configured with persistence enabled for the relevant data region, the node and cache are started, and your application has the correct cache handle. The exact setup and code depend on the language, cache configuration, and Ignite release; there is no single universally correct runnable snippet across Ignite clients.
Query records
Use Ignite’s SQL API or JDBC when you need conditions, selected fields, or tabular results rather than a single known key. A persistent cache does not make SQL fields or indexes automatic: verify the deployed cache’s schema and indexes, then run the query against Ignite.
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When the persistent store is an external database
Ignite’s CacheStore integration connects a cache to a separate RDBMS or NoSQL system. This is distinct from native persistence, which stores Ignite-managed partitions on disk. For external-store read-through, key-value operations can retrieve data that is not already in the cache: an individual get() can call load(), and getAll() can call loadAll().
If SQL must query those external records, load them into Ignite first. The documented preload methods are loadCache(), which loads on nodes where the cache is present, and localLoadCache(), which loads on one node. SQL SELECT does not retrieve absent rows directly from the external database.
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Use Index Reader only for offline inspection
If your goal is to diagnose data trees or check consistency between partition files and indexes, Ignite 2 provides the Index Reader command-line utility (index-reader.sh or index-reader.bat). The official documentation warns that the utility must be run against a persistent store that is not under a running grid. It is not a substitute for cache reads, SQL, or a supported routine way for an application to retrieve values.
Version and storage details to keep in mind
This procedure is specifically for Apache Ignite 2 native persistence. Ignite 3’s quick-start workflow describes RocksDB-based persistent storage, with data divided into partitions and separate disk files; its configuration and APIs should be taken from the documentation for the exact Ignite 3 version in use.
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Ignite 2’s storage internals explain why file-level inspection is different from ordinary reads: updates are appended to the write-ahead log (WAL), and checkpointing copies dirty pages from memory to partition files. These recovery and durability mechanisms do not change the application read path. The Ignite 2 tuning documentation gives DataStorageConfiguration.pageSize a default of 4 KB. It also describes Direct I/O as bypassing the operating-system file buffer cache and primarily as a checkpointing optimization; that configuration detail is not a guarantee of faster application queries.
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