Summary

__wt_btcur_skip_page() refuses to consider any internal page that is not in WT_REF_DISK:

if (F_ISSET(ref, WT_REF_FLAG_INTERNAL) && previous_state != WT_REF_DISK)
    goto unlock;

The reasoning is that an in-memory internal page cannot be judged by the aggregate in its address cell, because a descendant may be dirty with newer data than the aggregate reports and reconciliation is what propagates that upwards.

That reasoning does not hold for a clean in-memory internal page. Such a page carries no unreconciled data, so its address cell aggregate is as trustworthy as that of a page still on disk. It can be treated the same way an on-disk internal page already is, and become eligible for the walk skip. The leaf path already makes exactly this distinction through its clean_page handling; the internal path returns before reaching it.

The reviewer of PR #14629 asked for a separate ticket to skip clean in-memory internal pages in the tree walk.

Approach

• In __wt_btcur_skip_page() (src/include/btree_inline.h), stop returning early for an internal page in WT_REF_MEM that is not modified; let it fall through to the same address-cell evaluation used for WT_REF_DISK, reusing the existing clean_page determination.
• Establish the correctness condition precisely: the address cell aggregate of a clean internal page describes its state as of the last reconciliation, and a dirty descendant marks its ancestors dirty through __wt_page_modify_set(). Verify this holds on every path that can leave an ancestor clean above modified content, including split and instantiated-delete paths.
• Keep the existing state lock discipline: the decision is made under WT_REF_TRYLOCK so checkpoint and eviction cannot change the aggregate underneath.
• Account the skip through __wt_btcur_skip_page_inc() so the new case is visible in the walk-skip statistics.

Risk

Treating a clean internal page as on-disk is wrong if any descendant holds newer data than the aggregate reports; the walk would then silently hide live records. The visibility argument must be airtight before this lands, and the change should be exercised under format and the fast-truncate suites with eviction and checkpoint active.

Definition of done

• A clean in-memory internal page is evaluated through its address cell and skipped on the same terms as an on-disk internal page.
• A dirty internal page is still descended into.
• Test coverage that fails if the clean in-memory internal skip is applied where the subtree still holds visible records.