ElasticSearch Quality Control & Assurance 5

Question 1

How does the `_source` field configuration affect data quality and storage in Elasticsearch?

Accepted Answer

Disabling _source reduces heap usage but prevents document updates and reindexing

Answer

Disabling `_source` saves disk space but prevents `_update`, `update_by_query`, and reindex operations, which require the original document to be available.

Question 2

What is the role of the `_doc_count` field when performing quality checks on aggregation results from a rollup or summary index?

Accepted Answer

It tells Elasticsearch how many source documents a pre-aggregated bucket represents for accurate metric calculations

Answer

`_doc_count` allows a pre-summarized document to represent multiple source documents in aggregations, ensuring metrics like averages are computed correctly across rolled-up data.

Question 3

During a QA review of Elasticsearch mapping, you find `"index": false` on a field. What does this mean?

Accepted Answer

The field is stored but cannot be used in queries or filters

Answer

Setting `"index": false` means the field's values are stored in `_source` but not added to the inverted index, so it cannot be searched, filtered, or aggregated.

Question 4

Which Elasticsearch feature provides automatic quality enforcement by rejecting documents that would cause a shard's disk usage to exceed a configured limit?

Accepted Answer

Disk-based shard allocation with flood-stage watermark

Answer

The flood-stage watermark (default 95%) causes Elasticsearch to block writes to all indices on a node when disk usage is critically high, protecting node stability.

Question 5

What technique ensures that an Elasticsearch alias always points to the most current index while keeping historical data queryable?

Accepted Answer

Use `is_write_index: true` on one index in a multi-index alias

Answer

Marking one index as `is_write_index: true` in an alias directs all writes to that index while the alias can still span multiple indices for reads, supporting zero-downtime rollover.

ElasticSearch Practice Test

ElasticSearch Practice Test

ElasticSearch Quality Control & Assurance 5