overleaf/services/document-updater/app/coffee/DeleteQueueManager.js

/*
 * decaffeinate suggestions:
 * DS101: Remove unnecessary use of Array.from
 * DS102: Remove unnecessary code created because of implicit returns
 * DS207: Consider shorter variations of null checks
 * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
 */
let DeleteQueueManager;
const Settings = require('settings-sharelatex');
const RedisManager = require("./RedisManager");
const ProjectManager = require("./ProjectManager");
const logger = require("logger-sharelatex");
const metrics = require("./Metrics");
const async = require("async");

// Maintain a sorted set of project flushAndDelete requests, ordered by timestamp
// (ZADD), and process them from oldest to newest. A flushAndDelete request comes
// from real-time and is triggered when a user leaves a project. 
//
// The aim is to remove the project from redis 5 minutes after the last request
// if there has been no activity (document updates) in that time.  If there is
// activity we can expect a further flushAndDelete request when the editing user
// leaves the project. 
//
// If a new flushAndDelete request comes in while an existing request is already
// in the queue we update the timestamp as we can postpone flushing further.
//
// Documents are processed by checking the queue, seeing if the first entry is
// older than 5 minutes, and popping it from the queue in that case.

module.exports = (DeleteQueueManager = {
    flushAndDeleteOldProjects(options, callback) {
        const startTime = Date.now();
        const cutoffTime = (startTime - options.min_delete_age) + (100 * (Math.random() - 0.5));
        let count = 0;

        const flushProjectIfNotModified = (project_id, flushTimestamp, cb) => ProjectManager.getProjectDocsTimestamps(project_id, function(err, timestamps) {
            if (err != null) { return callback(err); }
            if (timestamps.length === 0) {
                logger.log({project_id}, "skipping flush of queued project - no timestamps");
                return cb();
            }
            // are any of the timestamps newer than the time the project was flushed?
            for (let timestamp of Array.from(timestamps)) {
                if (timestamp > flushTimestamp) {
                    metrics.inc("queued-delete-skipped");
                    logger.debug({project_id, timestamps, flushTimestamp}, "found newer timestamp, will skip delete");
                    return cb();
                }
            }
            logger.log({project_id, flushTimestamp}, "flushing queued project");
            return ProjectManager.flushAndDeleteProjectWithLocks(project_id, {skip_history_flush: false}, function(err) {
                if (err != null) {
                    logger.err({project_id, err}, "error flushing queued project");
                }
                metrics.inc("queued-delete-completed");
                return cb(null, true);
            });
        });

        var flushNextProject = function() {
            const now = Date.now();
            if ((now - startTime) > options.timeout) {
                logger.log("hit time limit on flushing old projects");
                return callback(null, count);
            }
            if (count > options.limit) {
                logger.log("hit count limit on flushing old projects");
                return callback(null, count);
            }
            return RedisManager.getNextProjectToFlushAndDelete(cutoffTime, function(err, project_id, flushTimestamp, queueLength) {
                if (err != null) { return callback(err); }
                if ((project_id == null)) { return callback(null, count); }
                logger.log({project_id, queueLength}, "flushing queued project");
                metrics.globalGauge("queued-flush-backlog", queueLength);
                return flushProjectIfNotModified(project_id, flushTimestamp, function(err, flushed) {
                    if (flushed) { count++; }
                    return flushNextProject();
                });
            });
        };

        return flushNextProject();
    },

    startBackgroundFlush() {
        const SHORT_DELAY = 10;
        const LONG_DELAY = 1000;
        var doFlush = function() {
            if (Settings.shuttingDown) {
                logger.warn("discontinuing background flush due to shutdown");
                return;
            }
            return DeleteQueueManager.flushAndDeleteOldProjects({
                timeout:1000,
                min_delete_age:3*60*1000,
                limit:1000 // high value, to ensure we always flush enough projects
            }, (err, flushed) => setTimeout(doFlush, (flushed > 10 ? SHORT_DELAY : LONG_DELAY)));
        };
        return doFlush();
    }
});