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Added a new file for explain method that is covered during skill badge
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‎java/105_aggregation_pipeline_explain.ipynb‎

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{
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"cells": [
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{
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"cell_type": "markdown",
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"id": "9d2c1c5d",
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"metadata": {},
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"source": [
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"[![Aggregation Pipeline Lab](https://img.shields.io/badge/Aggregation%20Pipeline%20Lab-darkgreen)](https://mongodb-developer.github.io/aggregation-pipeline-lab/)"
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]
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},
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{
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"cell_type": "markdown",
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"id": "3b936925-e295-489a-b508-2b99c0160217",
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"metadata": {},
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"source": [
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"# Aggregation Pipeline: explain()\n",
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" "
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]
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},
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{
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"cell_type": "markdown",
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"id": "4762f21c",
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"metadata": {},
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"source": [
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"## What does `explain()` do?\n",
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"\n",
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"`explain()` shows how MongoDB executes a query or aggregation pipeline. It is useful for understanding whether MongoDB is using an index and how much work the query performs.\n",
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"\n",
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"In this example, we will focus on two important fields:\n",
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"\n",
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"- `Index usage`: shows whether the query uses an index\n",
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"- `Execution time (ms)`: shows how long the query took to run\n",
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"\n",
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"We will run the same aggregation before and after creating an index, then compare the results."
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]
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},
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{
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"cell_type": "markdown",
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"id": "dependent-boundary",
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"metadata": {},
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"source": [
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"## Startup code"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"id": "66ef28c4-f86b-4576-839e-100a7ae022c7",
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"metadata": {},
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"outputs": [],
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"source": [
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"// Import the MongoDB Driver using Maven\n",
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"%maven org.mongodb:mongodb-driver-sync:5.5.1\n",
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"%maven org.slf4j:slf4j-simple:1.7.36\n",
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"\n",
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"import com.mongodb.ExplainVerbosity;\n",
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"import com.mongodb.client.AggregateIterable;\n",
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"import com.mongodb.client.MongoClient;\n",
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"import com.mongodb.client.MongoClients;\n",
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"import com.mongodb.client.MongoCollection;\n",
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"import com.mongodb.client.MongoDatabase;\n",
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"import com.mongodb.client.model.Indexes;\n",
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"import org.bson.Document;\n",
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"\n",
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"import java.util.List;\n",
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"\n",
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"import static com.mongodb.client.model.Aggregates.match;\n",
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"import static com.mongodb.client.model.Filters.and;\n",
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"import static com.mongodb.client.model.Filters.eq;\n",
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"\n",
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"// Configure SLF4J Simple Logger to suppress MongoDB driver logs in the notebook output.\n",
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"System.setProperty(\"org.slf4j.simpleLogger.defaultLogLevel\", \"off\");\n",
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"System.setProperty(\"org.slf4j.simpleLogger.log.org.mongodb.driver\", \"off\");\n",
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"\n",
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"// Set your connection String\n",
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"String connectionString = \"mongodb://admin:mongodb@localhost:27017/\";\n",
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"\n",
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"// Define our database and collection.\n",
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"MongoClient mongoClient = null;\n",
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"try {\n",
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" mongoClient = MongoClients.create(connectionString);\n",
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"} catch (Exception e) {\n",
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" System.out.println(e);\n",
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"}\n",
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"\n",
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"MongoDatabase library = mongoClient.getDatabase(\"library\");\n",
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"MongoCollection<Document> books = library.getCollection(\"books\");"
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]
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},
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{
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"cell_type": "markdown",
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"id": "d98078a6",
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"metadata": {},
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"source": [
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"## Before creating the index\n",
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"\n",
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"First, we run the aggregation with `explain()` to check the execution time and whether MongoDB uses an index."
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"id": "ab8508aa",
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"metadata": {},
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"outputs": [],
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"source": [
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"var filter = and(\n",
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" eq(\"title\", \"Collins Gem Italian Dictionary, 5e\"),\n",
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" eq(\"year\", 2001)\n",
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");\n",
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"\n",
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"var explainResult = books.aggregate(\n",
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" List.of(match(filter))\n",
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").explain(ExplainVerbosity.EXECUTION_STATS);\n",
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"\n",
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"System.out.println(\"Execution time (ms): \" +\n",
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" explainResult.get(\"executionStats\", Document.class).get(\"executionTimeMillis\"));\n",
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"\n",
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"System.out.println(\"Index usage: \" +\n",
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" explainResult.get(\"queryPlanner\", Document.class)\n",
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" .get(\"winningPlan\", Document.class)\n",
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" .toJson()\n",
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" .contains(\"IXSCAN\"));"
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]
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},
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{
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"cell_type": "markdown",
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"id": "c15e4530",
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"metadata": {},
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"source": [
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"## Create an index\n",
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"\n",
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"Now, we create an index on the fields used in the filter and list the indexes before and after the operation."
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"id": "31a0c996",
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"metadata": {},
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"outputs": [],
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"source": [
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"System.out.println(\"## Listing indexes\");\n",
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"books.listIndexes().forEach(System.out::println);\n",
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"\n",
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"System.out.println(\"Creating new index...\");\n",
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"books.createIndex(Indexes.ascending(\"title\", \"year\"));\n",
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"\n",
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"System.out.println(\"## Listing indexes\");\n",
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"books.listIndexes().forEach(System.out::println);"
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]
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},
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{
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"cell_type": "markdown",
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"id": "7604272c",
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"metadata": {},
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"source": [
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"## After creating the index\n",
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"\n",
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"Finally, we run the same aggregation again and compare the execution time and index usage."
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"id": "aea847d7",
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"metadata": {},
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"outputs": [],
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"source": [
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"var explainResult = books.aggregate(\n",
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" List.of(match(filter))\n",
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").explain(ExplainVerbosity.EXECUTION_STATS);\n",
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"\n",
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"System.out.println(\"Execution time (ms): \" +\n",
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" explainResult.get(\"executionStats\", Document.class).get(\"executionTimeMillis\"));\n",
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"\n",
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"System.out.println(\"Index usage: \" +\n",
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" explainResult.get(\"queryPlanner\", Document.class)\n",
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" .get(\"winningPlan\", Document.class)\n",
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" .toJson()\n",
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" .contains(\"IXSCAN\"));"
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]
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},
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{
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"cell_type": "markdown",
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"id": "f756ad70",
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"metadata": {},
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"source": [
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"## Summary\n",
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"\n",
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"With `explain()`, we can compare how MongoDB executes the same aggregation before and after creating an index. For basic performance analysis, two useful things to check are index usage and execution time."
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]
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Java",
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"language": "java",
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"name": "java"
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},
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"language_info": {
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"codemirror_mode": "java",
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"file_extension": ".jshell",
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"mimetype": "text/x-java-source",
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"name": "java",
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"pygments_lexer": "java",
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"version": "21.0.5+11-LTS"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 5
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}

java/105_aggregation_pipeline_merge.ipynb renamed to java/106_aggregation_pipeline_merge.ipynb

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