| /*------------------------------------------------------------------------- | |
| * | |
| * rmgrdesc_utils.h | |
| * Support functions for rmgrdesc routines | |
| * | |
| * Copyright (c) 2023, PostgreSQL Global Development Group | |
| * | |
| * src/include/access/rmgrdesc_utils.h | |
| * | |
| *------------------------------------------------------------------------- | |
| */ | |
| /* | |
| * Guidelines for rmgrdesc routine authors: | |
| * | |
| * The goal of these guidelines is to avoid gratuitous inconsistencies across | |
| * each rmgr, and to allow users to parse desc output strings without too much | |
| * difficulty. This is not an API specification or an interchange format. | |
| * (Only heapam and nbtree desc routines follow these guidelines at present, | |
| * in any case.) | |
| * | |
| * Record descriptions are similar to JSON style key/value objects. However, | |
| * there is no explicit "string" type/string escaping. Top-level { } brackets | |
| * should be omitted. For example: | |
| * | |
| * snapshotConflictHorizon: 0, flags: 0x03 | |
| * | |
| * Record descriptions may contain variable-length arrays. For example: | |
| * | |
| * nunused: 5, unused: [1, 2, 3, 4, 5] | |
| * | |
| * Nested objects are supported via { } brackets. They generally appear | |
| * inside variable-length arrays. For example: | |
| * | |
| * ndeleted: 0, nupdated: 1, deleted: [], updated: [{ off: 45, nptids: 1, ptids: [0] }] | |
| * | |
| * Try to output things in an order that faithfully represents the order of | |
| * fields from the underlying physical WAL record struct. Key names should be | |
| * unique (at the same nesting level) to make parsing easy. It's a good idea | |
| * if the number of items in the array appears before the array. | |
| * | |
| * It's okay for individual WAL record types to invent their own conventions. | |
| * For example, Heap2's PRUNE record descriptions use a custom array format | |
| * for the record's "redirected" field: | |
| * | |
| * ... redirected: [1->4, 5->9], dead: [10, 11], unused: [3, 7, 8] | |
| * | |
| * Arguably the desc routine should be using object notation for this instead. | |
| * However, there is value in using a custom format when it conveys useful | |
| * information about the underlying physical data structures. | |
| * | |
| * This ad-hoc format has the advantage of being close to the format used for | |
| * the "dead" and "unused" arrays (which follow the standard desc convention | |
| * for page offset number arrays). It suggests that the "redirected" elements | |
| * shown are just pairs of page offset numbers (which is how it really works). | |
| */ | |
| extern void array_desc(StringInfo buf, void *array, size_t elem_size, int count, | |
| void (*elem_desc) (StringInfo buf, void *elem, void *data), | |
| void *data); | |
| extern void offset_elem_desc(StringInfo buf, void *offset, void *data); | |
| extern void redirect_elem_desc(StringInfo buf, void *offset, void *data); | |
| extern void oid_elem_desc(StringInfo buf, void *relid, void *data); | |