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STORAGE Types

The STORAGE clause in the SELECT command, and the SUBSTRAT directive, accept one of the following identifiers. Each maps to a specific data-accessor class in the implementation.

Type table

KeywordC++ classRetentionShadowPurpose
DEFAULTgroupFile<posixBinaryFileWithShadow>yesyesDefault production mode; a .shadow file protects modifications
DIRECTgroupFile<posixBinaryFile>yesnoRetention without shadow protection
MEMORYmemoryFileyes (RAM)noData in memory only; circular buffer, never written to disk
POSIXposixBinaryFilenonoA single binary file; no retention
POSIXSHDposixBinaryFileWithShadownoyesA single file with shadow protection; no retention
GENERICgenericBinaryFilenonoGeneric binary file
DEVICEbinaryDeviceROnonoBinary device; read-only; looping depends on ONESHOT
TEXTSOURCEtextSourceROnonoText file; read-only; looping depends on ONESHOT

Retention — artifacts are rotated, older files are deleted automatically (requires RETENTION on SELECT).
Shadow — every modification is written to a separate .shadow file; historical data is protected from being overwritten.

For MEMORY, retention works in memory as a circular buffer: successive appends overwrite the oldest slot (index % capacity). Data is not segmented into files and never reaches disk.

NOTE: The MEMORY type (SUBSTRAT ‘memory’) is covered by the tests: issue61_tmpmem (serial and parallel), described in the appendix Integration Tests.

When to use which

The choice depends on the environment’s requirements:

  • Production environment, critical data → DEFAULT (retention + shadow)
  • Production environment, historically insignificant data → MEMORY (zero disk usage, retention in RAM)
  • Development and debugging → DEFAULT or DIRECT (data visible on disk)
  • Reading from a device or a text file → DEVICE / TEXTSOURCE (respectively)

Example

SELECT str1[0] STREAM str1 FROM core0 STORAGE MEMORY
SELECT str2[0] STREAM str2 FROM core0 RETENTION 100 STORAGE DIRECT

For substrates globally — the SUBSTRAT directive:

SUBSTRAT 'memory'