--- title: "formatReadableDecimalSize" slug: "dev-database-reference-sql-functions-numeric-formatreadabledecimalsize" updated: 2026-10-30T18:18:51Z published: 2026-10-30T18:18:51Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-numeric-formatreadabledecimalsize" --- > ## Documentation Index > Fetch the complete documentation index at: https://docs.vastdata.com/llms.txt > Use this file to discover all available pages before exploring further. # formatReadableDecimalSize *Applies to VAST Cluster 5.5.* *[Functions](/develop/docs/dev-database-reference-sql-functions-index) › [Numeric and math functions](/develop/docs/dev-database-reference-sql-functions-numeric) › Number formatting.* Writes a number of bytes for people to read, in decimal units of 1,000: `kB`, `MB`, `GB`, `TB` and `PB`. For binary units of 1,024, use [format_bytes](/develop/docs/dev-database-reference-sql-functions-numeric-format-bytes). ## Syntax ``` formatReadableDecimalSize(n) ``` | Argument | Type | Description | | --- | --- | --- | | `n` | An integer type up to `BIGINT` | A number of bytes. | **Returns:** `VARCHAR`. ## Set up the examples The examples connect with the ADBC driver, as in [VAST Query Engine (ADBC)](/develop/docs/dev-database-integrations-adbc), and work in a schema called `docs_sql_fn_numeric_formatreadabledecimalsize`. Set `QE_ENDPOINT`, `AWS_ACCESS_KEY_ID`, `AWS_SECRET_ACCESS_KEY` and `VASTDB_BUCKET` ([SQL reference](/develop/docs/dev-database-reference-sql-index#example-connect-and-use-a-transaction)), and run the blocks in order in one Python session. Below each block is the output you should see. This block connects, defines the `run()` and `plan()` helpers, and creates a table of six files with their sizes in bytes. The last row has no values: ``` import os import re import adbc_driver_manager import adbc_driver_manager.dbapi as dbapi import adbc_driver_vastdb BUCKET = os.environ["VASTDB_BUCKET"] SCHEMA = f'"{BUCKET}/docs_sql_fn_numeric_formatreadabledecimalsize"' conn = dbapi.connect( driver=adbc_driver_vastdb.get_driver_path(), db_kwargs={ "vast.db.endpoint": os.environ["QE_ENDPOINT"], "vast.db.access_key": os.environ["AWS_ACCESS_KEY_ID"], "vast.db.secret_key": os.environ["AWS_SECRET_ACCESS_KEY"], }, autocommit=True, ) def server_message(e): """The server's message in a driver error, without the request ID or the echoed statement.""" text = re.sub(r"\[req=0x[0-9a-f]+\]: ", "", str(e)) found = (re.search(r'message: "(.*?)", request_id', text, re.S) or re.search(r"description: (.*)\)", text, re.S)) message = found.group(1) if found else text.strip().splitlines()[-1] message = re.sub(r"^Plan query: '.*?' failed with: ", "", message, flags=re.S) message = re.split(r"\\n|\n", message)[0].replace('\\"', '"') return message.replace(BUCKET, "") def run(sql): """Run one statement. Print the rows it returns, or the error.""" try: with conn.cursor() as cur: cur.execute(sql) rows = cur.fetchall() if cur.description else [] except (adbc_driver_manager.Error, OSError) as e: print(f"{type(e).__name__}: {server_message(e)}") else: print(rows) def plan(sql): """Print the plan without its ~N Rows lines: the table's row count, which can still be 0 just after an insert.""" with conn.cursor() as cur: cur.execute("EXPLAIN " + sql) steps = cur.fetchall()[0][1] print("\n".join(line for line in steps.splitlines() if "Rows" not in line)) TABLE = f"{SCHEMA}.files" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, name VARCHAR, size_bytes BIGINT)") run(f"INSERT INTO {TABLE} VALUES " "(1, 'notes.txt', 1536), " "(2, 'photo.jpg', 5000000), " "(3, 'backup.tar', 3221225472), " "(4, 'empty.log', 0), " "(5, 'archive.parquet', 1125899906842624), " "(6, NULL, NULL)") ``` ``` [] [] [(6,)] ``` ## What it does `formatReadableDecimalSize(n)` divides `n` by 1,000 until it's below 1,000, or until it reaches `PB`, and writes the result with one decimal place and the unit. The kilobyte unit is written `kB`, with a lowercase `k`: | Call | Result | | --- | --- | | `formatReadableDecimalSize(1536)` | `'1.5 kB'` | | `formatReadableDecimalSize(5000000)` | `'5.0 MB'` | | `formatReadableDecimalSize(3221225472)` | `'3.2 GB'` | | `formatReadableDecimalSize(1099511627776)` | `'1.0 TB'` | | `formatReadableDecimalSize(1125899906842624)` | `'1.1 PB'` | Two details: - **Below 1,000 it writes whole bytes:** `'0 bytes'`, `'1 byte'`, `'999 bytes'`. - **The decimal is cut, not rounded:** `formatReadableDecimalSize(1075)` is `'1.0 kB'`, not `'1.1 kB'`, and `formatReadableDecimalSize(3221225472)` is `'3.2 GB'`. ## NULLs and edge cases | Input | Result | | --- | --- | | `NULL` | `NULL` | | `0`, `1`, `2` | `'0 bytes'`, `'1 byte'`, `'2 bytes'` | | `999`, `1000` | `'999 bytes'`, `'1.0 kB'` | | `1023`, `1024` | `'1.0 kB'`, `'1.0 kB'` | | `1075`, `1500` | `'1.0 kB'`, `'1.5 kB'` | | `1000000000000000000` (1,000 PB) | `'1000.0 PB'`: `PB` is the largest unit | | `9223372036854775807`, the largest `BIGINT` | `'9223.3 PB'` | | `1536::INTEGER`, `255::UTINYINT` | `'1.5 kB'`, `'255 bytes'` | | A `DECIMAL`, `DOUBLE` or `FLOAT` | Error: `No function matches the given name and argument types` | | A `UBIGINT` or `HUGEINT` | Error: `No function matches the given name and argument types` | | `'abc'` | Error: `Could not convert string 'abc' to INT64` | The same cases, as the cluster returns them. They use the table and helpers from [Set up the examples](/develop/docs/dev-database-reference-sql-functions-numeric-formatreadabledecimalsize#set-up-the-examples): ``` run("SELECT formatReadableDecimalSize(NULL), formatReadableDecimalSize(0), formatReadableDecimalSize(1), formatReadableDecimalSize(2)") run("SELECT formatReadableDecimalSize(999), formatReadableDecimalSize(1000), formatReadableDecimalSize(1023), formatReadableDecimalSize(1024)") run("SELECT formatReadableDecimalSize(1075), formatReadableDecimalSize(1500), formatReadableDecimalSize(1000000000000000000), formatReadableDecimalSize(9223372036854775807)") run("SELECT formatReadableDecimalSize(1536::INTEGER), formatReadableDecimalSize(255::UTINYINT)") run("SELECT formatReadableDecimalSize(1536.0::DOUBLE)") run("SELECT formatReadableDecimalSize(18446744073709551615::UBIGINT)") run(f"SELECT formatReadableDecimalSize('abc') FROM {TABLE} LIMIT 1") ``` ``` [(None, '0 bytes', '1 byte', '2 bytes')] [('999 bytes', '1.0 kB', '1.0 kB', '1.0 kB')] [('1.0 kB', '1.5 kB', '1000.0 PB', '9223.3 PB')] [('1.5 kB', '255 bytes')] InternalError: Binder Error: No function matches the given name and argument types 'formatReadableDecimalSize(DOUBLE)'. You might need to add explicit type casts. InternalError: Binder Error: No function matches the given name and argument types 'formatReadableDecimalSize(UBIGINT)'. You might need to add explicit type casts. OSError: Could not convert string 'abc' to INT64 ``` ## Examples The size of each file in decimal and in binary units: ``` run(f"SELECT id, name, formatReadableDecimalSize(size_bytes), format_bytes(size_bytes) FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, 'notes.txt', '1.5 kB', '1.5 KiB'), (2, 'photo.jpg', '5.0 MB', '4.7 MiB'), (3, 'backup.tar', '3.2 GB', '3.0 GiB'), (4, 'empty.log', '0 bytes', '0 bytes'), (5, 'archive.parquet', '1.1 PB', '1.0 PiB'), (6, None, None, None)] ``` The files of 1 GB or more. The condition is on the raw byte count, and `formatReadableDecimalSize()` only formats the rows returned: ``` run(f"SELECT id, name, formatReadableDecimalSize(size_bytes) FROM {TABLE} WHERE size_bytes >= 1000000000 ORDER BY id LIMIT 10") ``` ``` [(3, 'backup.tar', '3.2 GB'), (5, 'archive.parquet', '1.1 PB')] ``` The total size. `sum()` of a `BIGINT` column returns a `DECIMAL`, which `formatReadableDecimalSize()` doesn't take, so cast the sum to `BIGINT`: ``` run(f"SELECT formatReadableDecimalSize(CAST(sum(size_bytes) AS BIGINT)) FROM {TABLE}") ``` ``` [('1.1 PB',)] ``` ## How it runs in VAST The Query Engine runs on the cluster's CNodes, and a query on a table starts with a scan in VAST DataBase (`VAST_SCAN`). VAST DataBase can evaluate a comparison of a column with a constant, but not a function of a column, so `formatReadableDecimalSize()` is always computed by the Query Engine: - **In the `SELECT` list,** the scan reads the column and the Query Engine computes `formatReadableDecimalSize()` for each row it returns. - **In `WHERE`,** the scan sends the column for every row, and a `FILTER` step in the Query Engine computes `formatReadableDecimalSize()` and keeps the rows that match. No rows are skipped in storage. The plan of a `WHERE` condition on the function shows the `FILTER` step above the scan: ``` plan(f"SELECT id FROM {TABLE} WHERE formatReadableDecimalSize(size_bytes) IS NOT NULL") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ (formatReadableDecimalSize│ │ (size_bytes) IS NOT NULL) │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ size_bytes │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Filter on the byte count, not on the text.** `size_bytes >= 1000000000` is a comparison of the raw column with a constant, which is pushed down to VAST DataBase, so rows that don't match never leave storage. Its plan has no `FILTER` step: ``` plan(f"SELECT id FROM {TABLE} WHERE size_bytes >= 1000000000") ``` ``` ┌───────────────────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: id │ │ │ └───────────────────────────┘ ``` - **Format last.** Call `formatReadableDecimalSize()` in the `SELECT` list of the rows you return, and sort and compare on the number. ## Limitations and errors - **Integers up to `BIGINT`.** A `DECIMAL`, `DOUBLE` or `FLOAT` fails with `No function matches the given name and argument types`, and so do `UBIGINT` and `HUGEINT`. Cast the value to `BIGINT` first: `formatReadableDecimalSize(CAST(x AS BIGINT))`. This includes the result of `sum()` on an integer column. - **Decimal units only.** For units of 1,024 (`KiB`, `MiB`, `GiB`), use [format_bytes](/develop/docs/dev-database-reference-sql-functions-numeric-format-bytes). - **One decimal place, cut.** See [What it does](/develop/docs/dev-database-reference-sql-functions-numeric-formatreadabledecimalsize#what-it-does). ``` run("SELECT formatReadableDecimalSize(1.5)") run("SELECT formatReadableDecimalSize(CAST(1536.0 AS BIGINT))") ``` ``` InternalError: Binder Error: No function matches the given name and argument types 'formatReadableDecimalSize(DECIMAL(2,1))'. You might need to add explicit type casts. [('1.5 kB',)] ``` ## Similar functions | Function | Units | Result for `1536` | Result for `1500000` | | --- | --- | --- | --- | | `formatReadableDecimalSize` | 1,000: `kB`, `MB`, `GB`, `TB`, `PB` | `'1.5 kB'` | `'1.5 MB'` | | [format_bytes](/develop/docs/dev-database-reference-sql-functions-numeric-format-bytes), also `formatReadableSize` | 1,024: `KiB`, `MiB`, `GiB`, `TiB`, `PiB` | `'1.5 KiB'` | `'1.4 MiB'` | | [pg_size_pretty](/develop/docs/dev-database-reference-sql-functions-utility-pg-size-pretty) | 1,024 | `'1.5 KiB'` | | ``` run("SELECT formatReadableDecimalSize(1536), format_bytes(1536), formatReadableSize(1536), pg_size_pretty(1536)") run("SELECT formatReadableDecimalSize(1500000), format_bytes(1500000), formatReadableSize(1500000)") ``` ``` [('1.5 kB', '1.5 KiB', '1.5 KiB', '1.5 KiB')] [('1.5 MB', '1.4 MiB', '1.4 MiB')] ``` Clean up: ``` run(f"DROP TABLE IF EXISTS {TABLE}") run(f"DROP SCHEMA IF EXISTS {SCHEMA}") conn.close() ``` ``` [] [] ``` ## See also - [Numeric and math functions](/develop/docs/dev-database-reference-sql-functions-numeric): all the numeric functions. - [format_bytes](/develop/docs/dev-database-reference-sql-functions-numeric-format-bytes) and [pg_size_pretty](/develop/docs/dev-database-reference-sql-functions-utility-pg-size-pretty). - [Where filters run](/develop/docs/dev-database-reference-sql-select#where-filters-run) and [pushdowns](/develop/docs/dev-database-reference-pushdowns). - [EXPLAIN](/develop/docs/dev-database-reference-sql-explain): how to read a plan.