HboPinnedStatisticsLoader.java

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package org.apache.doris.nereids.stats;

import org.apache.doris.common.util.Daemon;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

/**
 * Loads the pinned hbo statistics this FE has persisted in
 * {@code __internal_schema.hbo_statistics} into memory, once, in the background.
 *
 * <p>The load is a DDL plus a full table scan, so it must not run on a user query's planning
 * thread: it would block that query for the duration of the internal statement and, worse, park
 * every other planner on the manager's monitor while it runs. It also must not run inside a
 * SET/DELETE which holds that monitor: the internal statement the load issues is planned like any
 * other query, and if hbo is enabled for the internal session its plan consults the pinned cache
 * again - re-entering the load in the middle of the memory update and the DB write of that
 * SET/DELETE (which could resurrect the very entry a DELETE just removed).
 *
 * <p>The daemon therefore owns the only call to the load. It retries every
 * {@link HboPlanStatisticsManager#LOAD_RETRY_INTERVAL_MS} until the entries are in memory (the
 * internal schema may not be ready right after start-up) and stops once the manager has everything
 * it needs, or once the internal schema database is disabled (a property of this FE which cannot
 * change at runtime). A FE whose persistence is merely configured off keeps the daemon cycling: the
 * load itself returns immediately in that case (no query is issued), and the cycle is what picks the
 * entries up when the operator turns the hot config on.
 */
public class HboPinnedStatisticsLoader extends Daemon {
    private static final Logger LOG = LogManager.getLogger(HboPinnedStatisticsLoader.class);

    private final HboPlanStatisticsManager manager;

    public HboPinnedStatisticsLoader(HboPlanStatisticsManager manager) {
        super("hbo-pinned-statistics-loader", HboPlanStatisticsManager.LOAD_RETRY_INTERVAL_MS);
        this.manager = manager;
    }

    @Override
    protected void runOneCycle() {
        if (!manager.needsPinnedStatisticsLoad()) {
            // either the entries are in memory, or nothing can be loaded on this FE (the internal
            // schema database is disabled): this thread has nothing left to do
            LOG.info("hbo pinned statistics loader stops, loaded={}", manager.isPinnedStatisticsLoaded());
            exit();
            return;
        }
        manager.loadPinnedStatistics();
    }
}