calculateStorageAndReusableSpace.js

/*
* Print storage details for all collections and indexes.
* Supports sharded clusters
*
* @author alex.bevilacqua@mongodb.com
* @version 1.3
* @updated 2022-11-21
*
* History:
* 1.3 - Filter out admin, local and config databases
* 1.2 - Properly filter out views
* 1.1 - Include Document Count / Average Object Size
* 1.0 - Initial Release
*/

var fmt = function (bytes) {
    // comment this out to format the results
    return bytes;

    var sizes = ['Bytes', 'KB', 'MB', 'GB', 'TB'];
    if (bytes == 0) return '0 Byte';
    var i = parseInt(Math.floor(Math.log(bytes) / Math.log(1024)));
    return Math.round(bytes / Math.pow(1024, i), 2) + ' ' + sizes[i];
}

var getDetail = function (label, stats) {
    var detail = {
        name: label,
        count: stats.count,
        avgSize: stats.avgObjSize,
        size: stats.size,
        storageSize: stats.storageSize,
        reusableSpace: stats.wiredTiger["block-manager"]["file bytes available for reuse"],
        indexSpace: stats.totalIndexSize,
        indexReusable: 0,
    };

    var indexKeys = Object.keys(stats.indexDetails);
    for (var i = 0; i < indexKeys.length; i++) {
        detail.indexReusable += stats.indexDetails[indexKeys[i]]["block-manager"]["file bytes available for reuse"];
    }

    return detail;
}

var dbSizeReport = function (dbname) {
    var results = []
    db.getSiblingDB(dbname).getCollectionInfos({ type: "collection" }, { nameOnly: true }).forEach(function(c) {    
        var coll = db.getSiblingDB(dbname).getCollection(c.name);
        var s = coll.stats({
            indexDetails: true
        });
        if (s.hasOwnProperty("sharded") && s.sharded) {
            var shards = Object.keys(s.shards);
            for (var i = 0; i < shards.length; i++) {
                var shard = shards[i];
                var shardStat = s.shards[shard];
                results.push(getDetail(s.ns + " (" + shard + ")", shardStat));
            }
        } else {
            results.push(getDetail(s.ns, s));
        }
    });

    var totals = [0, 0, 0, 0, 0];
    print(["Namespace", "Total Documents", "Average Document Size", "Uncompressed", "Compressed", "Reusable from Collections", "Indexes", "Reusable from Indexes"].join(","))
    for (var i = 0; i < results.length; i++) {
        var row = results[i];
        print([row.name, row.count, row.avgSize, fmt(row.size), fmt(row.storageSize), fmt(row.reusableSpace), fmt(row.indexSpace), fmt(row.indexReusable)].join(","))
        totals[0] += row.size;
        totals[1] += row.storageSize;
        totals[2] += row.reusableSpace;
        totals[3] += row.indexSpace;
        totals[4] += row.indexReusable;
    }

    print(["Total", "", "", fmt(totals[0]), fmt(totals[1]), fmt(totals[2]), fmt(totals[3]), fmt(totals[4])].join(","));
}

var IGNORE = ["admin", "local", "config"];
db.getMongo().getDBNames().forEach(function (dbname) {
    if (IGNORE.indexOf(dbname) < 0) {
        print("---------------------")
        print(dbname);
        print("---------------------")
        dbSizeReport(dbname);
    }
});

This script can be used to identify how much reclaimable space your MongoDB collections and indexes (using the WiredTiger storage engine) currently have. This space can be reclaimed using compact.

Sample output of this script:

---------------------
admin
---------------------
Namespace,Uncompressed,Compressed,Reusable from Collections,Indexes,Reusable from Indexes
admin.system.keys (config),255 Bytes,36 KB,16 KB,36 KB,16 KB
admin.system.version (config),59 Bytes,20 KB,0 Byte,20 KB,0 Byte
Total,314 Bytes,56 KB,16 KB,56 KB,16 KB
---------------------
config
---------------------
Namespace,Uncompressed,Compressed,Reusable from Collections,Indexes,Reusable from Indexes
config.actionlog (config),32 KB,40 KB,16 KB,40 KB,16 KB
config.changelog (config),346 KB,132 KB,52 KB,96 KB,44 KB
config.chunks (config),57 KB,52 KB,24 KB,144 KB,64 KB
config.collections (config),431 Bytes,36 KB,16 KB,36 KB,16 KB
config.databases (config),108 Bytes,20 KB,0 Byte,20 KB,0 Byte
config.lockpings (config),3 KB,36 KB,16 KB,72 KB,32 KB
config.locks (config),771 Bytes,36 KB,16 KB,108 KB,48 KB
config.migrations (config),0 Byte,24 KB,16 KB,48 KB,32 KB
config.mongos (config),342 Bytes,36 KB,16 KB,20 KB,0 Byte
config.settings (config),39 Bytes,20 KB,0 Byte,20 KB,0 Byte
config.shards (config),297 Bytes,20 KB,0 Byte,44 KB,4 KB
config.system.sessions (shard01),99 Bytes,36 KB,16 KB,60 KB,20 KB
config.tags (config),0 Byte,4 KB,0 Byte,24 KB,4 KB
config.transactions (config),0 Byte,24 KB,16 KB,12 KB,4 KB
config.version (config),83 Bytes,20 KB,0 Byte,20 KB,0 Byte
Total,441 KB,536 KB,204 KB,764 KB,284 KB
---------------------
test
---------------------
Namespace,Uncompressed,Compressed,Reusable from Collections,Indexes,Reusable from Indexes
test.test1 (shard01),37 MB,37 MB,27 MB,26 MB,16 MB
test.test1 (shard02),37 MB,8 MB,52 KB,5 MB,2 MB
test.test1 (shard03),38 MB,8 MB,56 KB,5 MB,2 MB
test.ups_test (shard01),0 Byte,24 KB,16 KB,72 KB,48 KB
Total,112 MB,54 MB,27 MB,36 MB,19 MB

If run within a sharded cluster, the Namespace will be followed by the shard name in parenthesis.