Reindexing data in Elasticsearch - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is reindexing in Elasticsearch?

Reindexing is the process of copying data from one index to another. It helps update or change the structure of data without losing it.

beginner

Which Elasticsearch API is used for reindexing data?

The _reindex API is used to copy documents from a source index to a destination index.

beginner

What is the basic JSON structure to reindex data from old_index to new_index?

{
  "source": { "index": "old_index" },
  "dest": { "index": "new_index" }
}

intermediate

How can you filter documents during reindexing?

You add a query inside the source to select only documents that match the filter.

beginner

Why might you want to reindex data in Elasticsearch?

To change mappings, update settings, fix errors, or move data to a new index without losing existing documents.

Which API is used to copy data from one Elasticsearch index to another?

A _delete

B _search

C _update

D _reindex

The _reindex API copies documents from a source index to a destination index.

What must you specify in the reindex request to select only some documents?

A query inside source

B dest index name

C script inside dest

D settings inside source

You add a query inside the source to filter which documents to reindex.

If you want to change the mapping of an index, what should you do?

A Delete the old index without backup

B Update the mapping directly on the old index

C Reindex data into a new index with the new mapping

D Use the _search API

Mappings cannot be changed directly; reindexing into a new index with updated mapping is the correct way.

What happens if you reindex without specifying a query?

A All documents from the source index are copied

B No documents are copied

C Only documents with errors are copied

D Only the first document is copied

Without a query, the _reindex API copies all documents from the source index.

Which of these is NOT a reason to reindex data?

A To fix mapping errors

B To delete documents permanently

C To update index settings

D To move data to a new index

Reindexing copies data; it does not delete documents permanently.

Explain how to perform a basic reindex operation in Elasticsearch.

Think about copying data from one place to another.

Describe why and when you would use reindexing in Elasticsearch.

Consider situations where data structure or location needs to change.