---
title: "Limits"
slug: "dev-database-reference-limits"
description: "Explore VAST Cluster 5.5 table size limits, structure combinations, and error handling for optimal database management and performance."
updated: 2026-10-30T18:18:46Z
published: 2026-10-30T18:18:46Z
canonical: "docs.vastdata.com/dev-database-reference-limits"
---

> ## 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.

# Limits

*Applies to VAST Cluster 5.5. Examples use the VAST DataBase Python SDK 2.1.0.*

This page lists the size and count limits of VAST DataBase tables in VAST Cluster 5.5, and which table structures you can combine: sorted tables, partitioned tables, semi-sorted projections, user-defined row IDs, vector indexes and replication.

## Sizes

| Limit | Value |
| --- | --- |
| Cell size, including metadata | 5 MB |
| Cell size for fixed-size binary columns | 64 KB |
| Cell size in a table with a semi-sorted projection | The 5 MB limit doesn't apply. Once a table has a projection, every cell in every column is limited to about 126 KB, including metadata, as before 5.5. Larger inserts fail with `SemiSortedIsNotSupportedWithLargeCells`, and `create_projection()` fails on a table that already holds larger cells. Dropping the projection lifts the limit. |
| Statement size | 5 MB |
| SDK request size | A query request (predicate and column list) may use up to about 90% of 5 MiB. Larger ones raise [TooLargeRequest](/develop/docs/dev-database-troubleshooting-errors#vastdberrorstoolargerequest-n-bytes). |
| User-defined row ID value | At most 2^47. See [User-defined row IDs](/docs-5-5/docs/user-defined-row-ids-for-tables). |

## Counts

| Limit | Value |
| --- | --- |
| Sort columns per table | Up to 4, and one sort order per table. A 5-column sorting key is rejected. |
| Partition keys per table | Up to 4. The SDK raises `ValueError` itself for more than 4. See [Database partitioning](/docs-5-5/docs/database-partitioning). |
| Rows before sorting takes effect | Tables are sorted in chunks of 512K rows, so smaller tables aren't effectively sorted. Sorting works best above 1 million rows. See [Sorted tables](/docs-5-5/docs/sorted-tables). |

**Cluster-wide maximums** (how many databases, tables, columns or snapshots a cluster can hold) are in the *VAST Cluster Scale Guidelines*, which aren't published on the KB (see [5.5.0 release notes](/docs-5-5/docs/vast-cluster-5-5-0-release-notes) and, for the maximum number of snapshots, [snapshots](/docs-5-5/docs/snapshots)). **Admin task: send to your platform team.** Ask for the Scale Guidelines values for your release.

## What can't be changed later

| Structure | Fixed at |
| --- | --- |
| Sorting | Once set, sorting can't be removed, and the sort columns and their order can't be changed. Values in sort columns can't be updated. See [Sorted tables](/docs-5-5/docs/sorted-tables). |
| Partitioning | Defined when the table is created; it can't be removed or changed. Partition columns can't be dropped, and their values can't be changed after insert, unless the update leaves the rows in the same partition. See [Database partitioning](/docs-5-5/docs/database-partitioning). |
| User-defined row IDs | If you supply row IDs in an insert, every later insert has to supply them too. See [User-defined row IDs](/docs-5-5/docs/user-defined-row-ids-for-tables). |

## Combining table structures

| Combination | Allowed? | Details |
| --- | --- | --- |
| Sorted + partitioned | Yes, at creation only | Set both in `create_table()`. You can't add sorting to an existing partitioned table. A column partitioned with the identity transform can't also be a sort column. A column partitioned with another transform, for example `day(ts)`, can be. See [Database partitioning](/docs-5-5/docs/database-partitioning). |
| Sorted + semi-sorted projection | No | In either order: you can't add a projection to a sorted table, or sort a table that has a projection. See [Sorted tables](/docs-5-5/docs/sorted-tables). |
| Sorted + user-defined row IDs | No | In either order. See [Sorted tables](/docs-5-5/docs/sorted-tables). |
| Sorted + vector index | No |  |
| Sorted + replication | No | You can't replicate a sorted table, or sort a replicated table. See [Sorted tables](/docs-5-5/docs/sorted-tables). |
| Partitioned + semi-sorted projection | No |  |
| Partitioned + user-defined row IDs | No |  |
| Partitioned + vector index | No | See [Database partitioning](/docs-5-5/docs/database-partitioning). |
| Partitioned + replication | No | See [Database partitioning](/docs-5-5/docs/database-partitioning). |
| Partitioned + quotas | Not supported | Quotas on partitioned tables aren't supported. Check with your platform team before you rely on a quota for a partitioned table. |
| Semi-sorted projection + user-defined row IDs | No | You can't add a projection to a table that uses user-defined row IDs. |
| Semi-sorted projection + vector index | Yes | A projection can be added to a vector-indexed table. |
| User-defined row IDs + vector index | No |  |
| Vector index + replication | No | You can't add a vector index to a table in a replicated path, or replicate a vector-indexed table. The error says "replication is currently not supported for vector indexed tables". |
| Semi-sorted projection + replication | Partly | The table replicates, but its semi-sorted projections aren't replicated. See [Overview of VAST Replication](/docs-5-5/docs/overview-of-vast-replication). |
| User-defined row IDs + replication | Not stated |  |

Plan the table structure before you create the table: most of these choices can't be changed later. [Data modeling](/develop/docs/dev-database-guides-data-modeling) explains how to choose.

### Errors when a combination isn't allowed

The cluster rejects the request when you try a combination that isn't allowed. These are the errors you'll see:

| Combination | Error |
| --- | --- |
| Sorted, partitioned or projection combinations | `BadRequest` (400), code `InvalidArgument`, message `Invalid Argument` |
| Any combination with user-defined row IDs | `BadRequest` (400), code `TabularRowAllocMethodConflict`, message `There is a conflict in tabular row allocation method` (with a vector index: `failed to enable vector index eres=106`) |
| Vector index with sorting or partitioning, at creation | `NotImplemented` (501), code `NotImplemented`, message `vector indexing cannot be combined with elysium sorting` or `... with partitioning` |

The `InvalidArgument` message doesn't say what's wrong. If you get it from `create_table()`, `add_sorting_key()` or `create_projection()`, check the table above first. "Elysium" in the message means sorted tables.

## Partition transforms

`create_table()` accepted each of these [PyIceberg transforms](https://py.iceberg.apache.org/) in a partition spec: identity, year, month, day, hour, bucket and truncate.