---
sourceDocument: Zurich ServiceNow AI Platform Administration
sourceDocumentLink: https://www.servicenow.com/docs/r/zurich/platform-administration

 Release :

    - zurich

ft:locale :

    - en-US

ft:publication_title :

    - Zurich ServiceNow AI Platform Administration

ft:clusterId :

    - platadm

bundleId :

    - platadm

workflow :

    - Platform


---

# Table flattening

# Table flattening {#ariaid-title1}

* Release version: Zurich
* 
* Updated July 31, 2025
* 
* ![](https://www.servicenow.com/docs/portal-asset/ico-clock) 3 minutes to read

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## Summary of Table flattening

Table flattening in ServiceNow stores a hierarchy of related tables as a single table within a relational database to improve query performance.
This approach addresses the performance challenges when querying complex table hierarchies by reducing or eliminating costly table joins.
Show full answer Show less  

## Extension Models

ServiceNow offers three extension models to store table hierarchies:

* **Table per class:** Each table in the hierarchy is stored in its own physical table. This is the default model used for most tables, including system tables. Queries involve joining multiple tables, which can lead to performance bottlenecks as the number of classes increases.
* **Table per hierarchy:** The entire hierarchy is stored in a single flat physical table named after the parent table. A class name column identifies the descendant table of each record. This model improves query performance by avoiding joins. It is used for the Task table hierarchy on MySQL databases. Use on Oracle databases requires contacting Technical Support.
* **Table per partition:** The hierarchy is stored in a single logical table that can have multiple physical partitions. Each partition optimizes database resource usage, such as column and index counts. Records include a class name and a class path column to efficiently constrain queries and enhance performance. This model is used for the Base Configuration Item (cmdb) table hierarchy on MySQL databases. Oracle support requires contacting Technical Support.

## Practical Implications for ServiceNow Customers

* Understanding the extension model used by your tables helps you anticipate query performance and database optimization needs.
* The default Table per class model is sufficient for most tables but can lead to slower queries on large hierarchies.
* Using Table per hierarchy or Table per partition models can significantly improve query performance for large, complex hierarchies like Task and CMDB tables, especially on MySQL databases.
* For Oracle databases, special arrangements via Technical Support are necessary to utilize the flattening models.
* Knowing your table's extension model enables effective performance tuning and maintenance planning.  
Table flattening stores a hierarchy of related tables as one table in a relational
database.

## Extension models {#c_TaskTableFlattening__section_lsz_nvx_cbb}

The system offers these extension models to store a table hierarchy on a relational database.  
{#c_TaskTableFlattening__table_chh_wbf_dbb__entry__2}

| Extension model | Flattens tables? |
|-|-|
| Table per class | No |
| Table per hierarchy | Yes |
| Table per partition | Yes |
[Table 1. Available extension models]

{#c_TaskTableFlattening__table_chh_wbf_dbb}

## Table per class {#c_TaskTableFlattening__section_gcd_t2y_cbb}

The Table per class extension model stores each table of the hierarchy in its own
physical table on the relational database. Each physical table uses the table prefix of the
source table each stores a different class of records. An example of the Table per class
extension model is the Asset \[alm_asset\] table, and its child tables: Hardware \[alm_hardware\],
Consumable \[alm_consumable\], Facility \[alm_facility\], and Software License \[alm_license\]. The
parent table of the hierarchy, Asset, stores a copy of every record in its descendant
tables.

To find records in the Table per class extension model, the system queries records from
multiple tables and joins the results. For example, when searching for hardware in a related
facility, the system must join results from the Hardware, Facility, and Asset tables.

Table joins cause a performance bottleneck on relational databases. The more classes a query
includes, the worse the query performance. Therefore any query for records from the top of the
table hierarchy has the worst performance because it requires joining all descendant tables.

The system uses the Table per class extension model by default when creating tables. Most
system tables also use the Table per class extension model as there is no performance benefit
from flattening them.

## Table per hierarchy {#c_TaskTableFlattening__section_qqk_52y_cbb}

The Table per hierarchy extension model stores an entire table hierarchy in a
single flat physical table on the relational database. The physical table is named after the
parent table of the hierarchy, such as Task. The physical table contains all records of the
table hierarchy and assigns a class name column value to each descendant table of the hierarchy.
The system uses the name of the source table as the class name value. For example, Task records
can have class names such as Change, Incident, or Problem.

To find records in a table hierarchy, the system queries the physical table and uses the class
name column to constrain the results. Since such queries do not require joining results from
multiple tables, the system provides better search performance.

The system uses the Table per hierarchy extension model for the Task table hierarchy on MySQL
databases. Other tables use the Table per class extension model because there is no performance
benefit to flattening them. To use Table per hierarchy on an Oracle database, contact Technical
Support.

## Table per partition {#c_TaskTableFlattening__section_d5h_v2y_cbb}

The Table per partition extension model stores an entire table hierarchy in a
single flat logical table on the relational database. Each logical table can have multiple
physical storage tables called partitions supporting it. Each partition optimizes
the database resources available to a physical table such as the column count, index count, and
row size. The system adds a partition whenever the logical table needs additional relational
database resources.

Each logical table is named after the parent table of the hierarchy, and each supporting
physical partition consists of the logical name plus a partition name. For example, the Base
Configuration Item \[cmdb\] table starts as a logical table with no partitions. Suppose your
hardware configuration items consume enough database resources that the system creates a
partition called cmdb$par1 to store them. Later, computer configuration
items could consume enough database resources to warrant the system creating a second partition
called cmdb$par2 to store these records.

Within each logical table, the system assigns a class name column value to each descendant
table of the hierarchy. For example, within the Base Configuration Item logical table there are
records with class names for Application, Computer, and IP Router. The system also assigns a
two-digit class path value to each descendant table of the hierarchy. The class path is based on
the table location in the hierarchy. For example, the parent class Hardware might have a class
path such as /!!/!D and the child class Computer might have a class path
such as /!!/!D/!!.

To find records in the Table per partition extension model, the system queries the logical
table and its partitions and uses the class path column to constrain the results. Since these
queries do not require joining results from multiple tables, the system provides better search
performance. In addition, the class path reduces the total number of records to search, which
further improves search performance.

The system uses the Table per partition extension model for the Base Configuration Item \[cmdb\]
table hierarchy on MySQL databases. To use Table per partition on an Oracle database, contact
Technical Support.
* **[View a table hierarchy and the extension model](https://www.servicenow.com/docs/_7JX6D2IYky6FzXLzj1N1A)**   
  Determine the extension model used by a table.