Function write_index_btree

internal/cbm/sqlite_writer.c:1280–1341

Write leaf pages for an index, returns root page.

// Write leaf pages for an index, returns root page.
static uint32_t write_index_btree(FILE *fp, uint32_t *next_page, uint8_t **cells, int *cell_lens,
                                  int count) {
    if (count == 0) {
        return write_empty_index_leaf(fp, next_page);
    }

    /* Spill oversized index payloads to overflow pages BEFORE page building so
     * every cell added below is within the local-payload limit (see
     * INDEX_OVERFLOW_MAX_LOCAL). Overflow pages are allocated from *next_page
     * ahead of the leaf pages, which is fine — page order is arbitrary. */
    for (int i = 0; i < count; i++) {
        cells[i] = overflowize_index_cell(fp, next_page, cells[i], &cell_lens[i]);
    }

    PageBuilder pb;
    pb_init(&pb, fp, *next_page, true);

    for (int i = 0; i < count; i++) {
        if (!pb_cell_fits(&pb, cell_lens[i])) {
            if (pb.cell_count > 0) {
                if (!pb_promote_and_flush(&pb, cells, cell_lens, i - SKIP_ONE)) {
                    return 0;
                }
            }
            // After flush, check if the cell still doesn't fit on an empty page.
            // Index cells larger than a full page can never be stored; skip them.
            if (!pb_cell_fits(&pb, cell_lens[i])) {
                (void)fprintf(stderr, "cbm_write_db: index cell oversized, skipped len=%d idx=%d\n",
                              cell_lens[i], i);
                continue;
            }
        }
        pb_add_cell(&pb, cells[i], cell_lens[i]);
    }

    if (pb.cell_count > 0) {
        if (!pb_ensure_leaf_cap(&pb)) {
            return 0;
        }
        pb.leaves[pb.leaf_count].max_key = 0;
        int last = count - SKIP_ONE;
        pb.leaves[pb.leaf_count].sep_cell = (uint8_t *)malloc(cell_lens[last]);
        memcpy(pb.leaves[pb.leaf_count].sep_cell, cells[last], cell_lens[last]);
        pb.leaves[pb.leaf_count].sep_cell_len = cell_lens[last];
        pb_flush_leaf(&pb);
    }

    *next_page = pb.next_page;

    uint32_t root;
    if (!pb.leaves) {
        root = 0;
    } else if (pb.leaf_count == SKIP_ONE) {
        root = pb.leaves[0].page_num;
    } else {
        root = pb_build_interior(&pb, true);
        *next_page = pb.next_page;
    }