Batch Import

Performance Differences and Their Causes

When importing multiple updates into a document, using doc.importBatch(updates) is significantly faster than importing updates individually. This performance difference stems from how data merging is handled in each approach.

const doc = new LoroDoc();
doc.getText("text").update("Hello");
const update1 = doc.export({ mode: "update" });
const version = doc.version();
doc.getText("text").update("Hello World");
const update2 = doc.export({ mode: "update", from: version });
 
const newDoc1 = new LoroDoc();
newDoc1.importBatch([update1, update2]); // faster
 
const newDoc2 = new LoroDoc();
for (const update of [update1, update2]) { // slower
  newDoc2.import(update);
}

Key Advantages of Import Batch

1. Single Diff Calculation

The most significant advantage is that import batch performs only one diff calculation. In contrast, each individual import follows these steps:

• Merge remote updates into local history
• Calculate document state changes from the current version to the merged version
• Apply the diff to the current document state

This diff calculation has fixed overhead costs that accumulate with each import. But doc.importBatch(...) only performs one diff calculation, which is faster than multiple individual diff calculations.

2. Reduced Communication Overhead

Import batch also results in more concise events. Each individual import generates a new event, but doc.importBatch(...) generates only a single event that contains all the changes.