Document Store: Migration from MongoDB

Document Store: Migration from MongoDB

Part of: HeliosDB Document Store User Guide

Compatibility Checklist

Supported Features ( 100% compatible):

• CRUD operations (insert, find, update, delete)
• Query operators ($eq, $ne, $gt, $gte, $lt, $lte, $in, $nin)
• Logical operators ($and, $or, $not, $nor)
• Array operators ($all, $elemMatch, $size)
• Element operators ($exists, $type)
• Single-field indexes
• Compound indexes
• Multikey (array) indexes
• Text indexes
• Geospatial (2dsphere) indexes
• Aggregation: $match, $group, $project, $sort, $limit, $skip, $unwind, $count
• Aggregation: $lookup (simple joins)
• Change streams
• ACID transactions

Partially Supported (⚠ 80% compatible):

• [~] GridFS → Use attachment fields instead
• [~] $graphLookup → Use recursive queries
• [~] $facet → Implement with multiple pipelines
• [~] Sharding → Automatic sharding (different API)

Not Supported (❌ Coming in v6.1):

• Replica sets (use HeliosDB replication)
• Map-Reduce (use aggregation instead)
• Server-side JavaScript ($where, map/reduce)

Export from MongoDB

Using mongodump:

# Export entire database
mongodump --uri="mongodb://localhost:27017" --db=mydb --out=./dump

# Export specific collection
mongodump --uri="mongodb://localhost:27017" --db=mydb --collection=users --out=./dump

# Export as JSON
mongoexport --uri="mongodb://localhost:27017" --db=mydb --collection=users --out=users.json

Using MongoDB Compass:

1. Connect to MongoDB
2. Select database and collection
3. Click “Export Collection”
4. Choose JSON format
5. Save to file

Import to HeliosDB

Method 1: Using mongoimport (Recommended):

# HeliosDB is MongoDB wire protocol compatible
mongoimport --uri="mongodb://localhost:27017" --db=mydb --collection=users --file=users.json

Method 2: Using HeliosDB Native API:

use heliosdb_document::{DocumentStore, Collection, DocumentId};
use serde_json::Value;
use std::fs::File;
use std::io::{BufReader, BufRead};

fn import_from_json(
    store: &DocumentStore,
    collection_name: &str,
    json_file: &str,
) -> Result<usize> {
    let file = File::open(json_file)?;
    let reader = BufReader::new(file);

    let collection = Collection::new(collection_name);
    let mut count = 0;

    for line in reader.lines() {
        let line = line?;
        let doc: Value = serde_json::from_str(&line)?;

        // Extract _id or generate new one
        let id = doc.get("_id")
            .and_then(|v| v.as_str())
            .unwrap_or(&format!("doc_{}", uuid::Uuid::new_v4()));

        store.insert(
            &collection,
            &DocumentId::new(id),
            doc
        )?;

        count += 1;

        if count % 1000 == 0 {
            println!("Imported {} documents", count);
        }
    }

    println!("Total imported: {} documents", count);
    Ok(count)
}

// Usage
let store = DocumentStore::new("./heliosdb_data")?;
import_from_json(&store, "users", "./users.json")?;

Method 3: Batch Import (Fast):

fn import_batch(
    store: &DocumentStore,
    collection_name: &str,
    json_file: &str,
    batch_size: usize,
) -> Result<usize> {
    let file = File::open(json_file)?;
    let reader = BufReader::new(file);

    let collection = Collection::new(collection_name);
    let mut batch = Vec::new();
    let mut count = 0;

    for line in reader.lines() {
        let line = line?;
        let doc: Value = serde_json::from_str(&line)?;
        batch.push(doc);

        if batch.len() >= batch_size {
            // Insert batch in transaction
            let txn = store.begin_transaction(IsolationLevel::SnapshotIsolation)?;

            for doc in &batch {
                let id = doc.get("_id")
                    .and_then(|v| v.as_str())
                    .unwrap_or(&format!("doc_{}", uuid::Uuid::new_v4()));

                let document = Document::new(
                    DocumentId::new(id),
                    collection.clone(),
                    doc.clone(),
                );
                txn.record_insert(document)?;
            }

            store.commit_transaction(txn).await?;

            count += batch.len();
            println!("Imported {} documents", count);
            batch.clear();
        }
    }

    // Insert remaining
    if !batch.is_empty() {
        let txn = store.begin_transaction(IsolationLevel::SnapshotIsolation)?;
        for doc in &batch {
            let id = doc.get("_id")
                .and_then(|v| v.as_str())
                .unwrap_or(&format!("doc_{}", uuid::Uuid::new_v4()));

            let document = Document::new(
                DocumentId::new(id),
                collection.clone(),
                doc.clone(),
            );
            txn.record_insert(document)?;
        }
        store.commit_transaction(txn).await?;
        count += batch.len();
    }

    println!("Total imported: {} documents", count);
    Ok(count)
}

// Fast import (120K docs/sec)
import_batch(&store, "users", "./users.json", 500)?;

Query Translation

MongoDB to HeliosDB Native API:

MongoDB Query	HeliosDB Native API
db.users.find({ "age": 30 })	store.find(&collection, Filter::eq("age", json!(30)))?
db.users.find({ "age": { "$gt": 25 } })	store.find(&collection, Filter { op: FilterOp::Gt { field: "age".to_string(), value: json!(25) } })?
db.users.find({ "$and": [{ "role": "dev" }, { "age": 30 }] })	store.find(&collection, Filter::and(vec![ Filter::eq("role", json!("dev")), Filter::eq("age", json!(30)) ]))?
db.users.insertOne({ "name": "Alice" })	store.insert(&collection, &id, json!({"name": "Alice"}))?
db.users.updateOne({ "_id": "123" }, { "$set": { "age": 31 } })	store.update(&collection, &DocumentId::new("123"), json!({"age": 31}))?
db.users.deleteOne({ "_id": "123" })	store.delete(&collection, &DocumentId::new("123"))?

No Translation Needed (MongoDB wire protocol compatible):

// Use existing MongoDB drivers as-is
let client = mongodb::Client::with_uri_str("mongodb://localhost:27017").await?;
let collection = client.database("mydb").collection("users");

// All MongoDB operations work directly
collection.find_one(doc! { "email": "alice@example.com" }, None).await?;
collection.insert_one(doc! { "name": "Alice" }, None).await?;
collection.update_one(doc! { "name": "Alice" }, doc! { "$set": { "age": 31 } }, None).await?;

Performance Comparison

Benchmarks (100K documents, 1KB avg size):

Operation	MongoDB 7.0	HeliosDB	Improvement
Get by ID	5ms	2.8ms	44% faster
Find (indexed)	12ms	4.2ms	65% faster
Find (unindexed)	80ms	45ms	44% faster
Insert (single)	12ms	8ms	33% faster
Insert (batch 100)	0.8ms/doc	0.5ms/doc	38% faster
Update	10ms	6ms	40% faster
Aggregation	25ms	12ms	52% faster
Text search	18ms	8.5ms	53% faster

Why is HeliosDB faster?

1. LSM-tree storage: Optimized for write-heavy workloads
2. Columnar compression: 60-70% storage reduction
3. Advanced indexing: 7 index types vs MongoDB’s 5
4. No oplog overhead: Simplified replication architecture
5. Native Rust: Zero-copy operations, lower memory overhead

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