Merge health and part backlog

Answers "are merges running, for which tables, and what is holding them back?" from system.merges, system.part_log and system.parts. Run altinity-expert-clickhouse-connection first if the connection mode, cluster and time window are not yet established.

Query packs

• checks.sql — 8 checks: current merge activity with memory, algorithm and type (merges-01), active merge memory per host and cluster-wide (merges-02, merges-03), merge success/failure trend by hour (merges-04), table-level merge verdict (merges-05), merge reason and algorithm matrix (merges-06), peak merge RAM per table (merges-07), part-count offenders (merges-08). Checks merges-04 through merges-07 need system.part_log.
• reference.md — background (merge and TTL settings, ad-hoc query safeguards); read only when you need to explain a recommendation.

How to run the query packs

1. Read each pack file from this skill's directory (the skill loader prints the directory path).
2. Run statements one at a time, never a whole file. Statements end with ; and start with a -- @check <id> <title> header; keep the id with its result.
3. Honor -- @requires: skip the statement when the named table is missing, when keeper is required and the server has no Keeper/ZooKeeper, or when the version condition is not met. List skipped ids with the reason.
4. Keep {cluster} as written when a cluster macro exists; otherwise apply the connection skill's rewrite rule. Any other {placeholder} is a template variable: substitute a real value first or skip the statement.
5. On an error, record the check id and the first line of the error, then continue. Only for UNKNOWN_IDENTIFIER, run DESCRIBE TABLE system.<table> and drop the missing column.
6. A severity column is the verdict for that row. Copy it; do not re-grade.