Copyright and License

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Global Handler

The database is organized in a B* tree structure in disk files, each file directly corresponding to a single M global.

On-disk, the arrangement is /var/local/freem/<namespace-name>/<global-name>, where <global-name> would be something like ^DD.

Percent globals (^%…) conventionally reside in the SYSTEM namespace.

Non-percent globals (^…) reside in other namespaces, or the USER namespace by default.

Blocks

Blocks are BLOCKLEN bytes long (1024 in the current implementation).

Relevant Source Files

global.c (see especially the function global())

Relevant Constants

Block Offsets

Each of the following constants describe a byte offset to a particular type of data within a single block.

| CONSTANT | DESCRIPTION                                    | BLOCK TYPE       |
+----------+------------------------------------------------+------------------+
| LLPTR    | Left-Link Pointer                              | DATA, PTR, BPTR  |
| RLPTR    | Right-Link Pointer                             | DATA, PTR, BPTR  |
| NRBLK    | Number of Blocks                               | ROOT             |
| COLLA    | Collation (1: numeric, 2: alphabetical)        | ROOT             |
| FREE     | Free Block Count                               | ROOT             |
| BTYP     | Block Type (2: PTR, 6: BPTR, 8: DATA)          | ALL              |
| OFFS     | Offset to Unused Portion of Data Area          | ALL              |

Other Constants

| CONSTANT | DESCRIPTION                                    |
+----------+------------------------------------------------+
| DATALIM  | Length of block data area (offsets 0-1013)     |
| BLOCKLEN | Length of block (currently 1024)               |

Root Block Format

| STARTING OFFSET   | ENDING OFFSET    | DESCRIPTION                         |
+-------------------+------------------+-------------------------------------+
| 0                 | 1013 (DATALIM)   | Block Data Area                     |
| 1014 (NRBLK)      | 1016             | Number of Blocks                    |
| 1017 (COLLA)      | 1017             | Collation (0 numeric, 1 alpha)      |
| 1018 (FREE)       | 1020             | Free Block Count                    |
| 1021 (BTYP)       | 1021             | Block Type (2 PTR 6 BPTR 8 DATA)    |
| 1022 (OFFS)       | 1023             | Ptr to free part of block data area |

Data Block Format

| STARTING OFFSET   | ENDING OFFSET    | DESCRIPTION                          |
+-------------------+------------------+--------------------------------------+
| 0                 | 0                | Length of Key - Offset to Prev. Key  |
| 1                 | 1                | Offset to Prev. Key                  |
| 2                 | < DATALIM        | Compressed Key                       |
| <VARIES>          | < DATALIM        | Length of Global Data (2 bytes)      |
| <VARIES>          | < DATALIM        | Global Data                          |
| 1014 (LLPTR)      | 1016             | Left-Link Pointer                    |
| 1017              | 1017             | <RESERVED>                           |
| 1018 (RLPTR)      | 1020             | Right-Link Pointer                   |
| 1021 (BTYP)       | 1021             | Block Type (2: PTR, 6: BPTR, 8: DATA)|
| 1022 (OFFS)       | 1023             | Ptr to free part of block data area  |

Pointer Block Format

| STARTING OFFSET   | ENDING OFFSET    | DESCRIPTION                          |
+-------------------+------------------+--------------------------------------+
| 0                 | 0                | Length of Key - Offset to Prev. Key  |
| 1                 | 1                | Offset to Prev. Key                  |
| 2                 | < DATALIM        | Compressed Key                       |
| <VARIES>          | (2 Bytes)        | Forward Pointer (to ptr or data blk) |
| 1017              | 1017             | <RESERVED>                           |
| 1021 (BTYP)       | 1021             | Block Type (2 or 6)                  |
| 1022 (OFFS)       | 1023             | Ptr to free part of block data area  |