---
type: concept
x-llmwiki:
  schemaVersion: "0.1"
  contentHash: ec25b6a76a5eff340a9956d230bed9c605c9e3ea135a20ebe28ba67f27fa8e8f
  pageDirectory: concepts
  sources:
    - convert-to-delta-databricks-on-aws.md
  confidence: 1
  provenanceState: extracted
  freshnessStatus: unverified
  aliases:
    - statistics-collection-during-delta-conversion
    - SCDDC
  citations:
    - file: convert-to-delta-databricks-on-aws.md
title: Statistics Collection during Delta Conversion
description: The process of collecting statistics during CONVERT TO DELTA to improve query performance, which can be bypassed with the NO STATISTICS option.
tags:
  - delta-lake
  - performance
  - statistics
timestamp: "2026-06-19T17:52:36.869Z"
---

# Statistics Collection during Delta Conversion

**Statistics Collection during Delta Conversion** refers to the process that `CONVERT TO DELTA` performs when transforming an existing Parquet table (or an Apache Iceberg table with Parquet underlying files) into a [Delta Lake](/concepts/delta-lake.md) table. During conversion, the command reads the footers of all Parquet files to infer the schema and collects statistics to improve query performance on the resulting Delta table.^[convert-to-delta-databricks-on-aws.md]

## How Statistics Are Collected

The `CONVERT TO DELTA` command automatically infers the data schema by reading the footers of every Parquet file in the source directory. After listing all files in the directory, it creates a Delta Lake transaction log that tracks these files and simultaneously gathers statistics. These statistics enable query optimizations such as data skipping and predicate pushdown on the converted table.^[convert-to-delta-databricks-on-aws.md]

For Iceberg tables, the converter generates the Delta Lake transaction log based on the Iceberg table's native file manifest, schema, and partitioning information.^[convert-to-delta-databricks-on-aws.md]

## The NO STATISTICS Option

The `NO STATISTICS` clause can be appended to the `CONVERT TO DELTA` command to bypass statistics collection entirely. This accelerates the conversion process because the command no longer reads the file contents to compute statistics. However, after the table is converted, query performance may be suboptimal until statistics are generated by other means.^[convert-to-delta-databricks-on-aws.md]

Syntax example:

```sql
CONVERT TO DELTA parquet.`s3://my-bucket/path/to/table` NO STATISTICS;
```

## Performance Recommendations

Databricks recommends that after converting a table to Delta Lake — especially when `NO STATISTICS` is used — you use [Liquid Clustering](/concepts/liquid-clustering.md) to reorganize the data layout and generate fresh statistics. This helps restore the query performance that statistics enable.^[convert-to-delta-databricks-on-aws.md]

For tables that have been converted without statistics, consider running `OPTIMIZE` with liquid clustering to rebuild statistics and improve query efficiency.

## Behavior with Metastore-Only Tables

For tables registered to the [Metastore](/concepts/metastore.md), `CONVERT TO DELTA` also updates the [Metastore](/concepts/metastore.md) to reflect that the table is now a Delta table. The partition specification is loaded from the [Metastore](/concepts/metastore.md) when the `table_name` is a qualified table identifier.^[convert-to-delta-databricks-on-aws.md]

## Related Concepts

- [Delta Lake](/concepts/delta-lake.md) — The storage layer that manages the transaction log and statistics
- [Liquid Clustering](/concepts/liquid-clustering.md) — Recommended method to reorganize data and generate statistics after conversion
- [CONVERT TO DELTA](/concepts/convert-to-delta.md) — The full command syntax and parameters
- VACUUM — Cleanup operation that removes files not tracked by Delta Lake
- Parquet — The source file format for conversion
- Iceberg — Alternative table format that can be converted when its underlying files are Parquet

## Sources

- convert-to-delta-databricks-on-aws.md

# Citations

1. [convert-to-delta-databricks-on-aws.md](/references/convert-to-delta-databricks-on-aws-4b099753.md)
