---
name: "pmaDeltaInDom"
section: "3"
platform: "linux"
package: "pcp"
version: "7.2.2-2"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/pmaDeltaInDom"
---

# pmaDeltaInDom(3)

generate a \`\`delta indom'' if two observations of an instance domain are different

## NAME

**pmaDeltaInDom** - generate a \`\`delta indom'' if two observations of an instance domain are different

## C SYNOPSIS

**#include \<pcp/pmapi.h\>**\
 **#include \<pcp/libpcp.h\>**\
 **#include \<pcp/archive.h\>**

**int pmaDeltaInDom(\_\_pmLogInDom \****old***,** **\_\_pmLogInDom \****new***,** **\_\_pmLogInDom \****new\_delta***);**

**cc ... -lpcp\_archive -lpcp**

## CAVEAT

This documentation is intended for internal Performance Co-Pilot (PCP) developer use.

These interfaces are not part of the PCP APIs that are guaranteed to remain fixed across releases, and they may not work, or may provide different semantics at some point in the future.

## DESCRIPTION

Checks if two observations of the same instance domain are identical, and if they are **not**, tries to generate a \`\`delta indom'' to describe the differences.

The code assumes (a) *old*-\>*indom* == *new*-\>*indom* and (b) both the instance domains are sorted in ascending internal instance identifier sequence; see [**pmaSortInDom**(3)](/pmaSortInDom/3.md) to see how to make the second condition true.

The \`\`delta indom'' format is only supported for Version 3 archives and it is the caller's responsibility to determine if calling **pmaDeltaInDom** is appropriate, rather than calling [**pmaSameInDom**(3)](/pmaSameInDom/3.md) which is the preferred method for V2 archives.

**pmaDeltaInDom** returns 0 if the *old* and *new* instance domains are the same.

A return value of 1 indicates that the instance domains are different and the \`\`delta indom'' format is **not** more efficient; in this case *new\_delta* is not modified.

A return value of 2 indicates that the instance domains are different and *new\_delta* has been set up to describe the \`\`delta indom'' encoding of the differences;  in this case the caller is responsible for freeing *new\_delta*-\>*instlist* and *new\_delta*-\>*namelist.*

The instance domains are considered different if any of the following hold:

- 1\.

  *old*-\>*numinst* != *new*-\>*numinst*

- 2\.

  For some i, *old*-\>*instlist*\[*i*\] *!=* new*-\>*instlist*\[*i*\]*

- 3\.

  For some i, the strings pointed to by *old*-\>*namelist*\[*i*\] and *new*-\>*instlist*\[*i*\] are not identical

## DELTA INDOM FORMAT

As for a regular instance domain, *new\_delta*-\>*numinst* defines the number of instance specifications.

If *new\_delta*-\>*namelist*\[*i*\] == NULL then the instance identified by *new\_delta*-\>*instlist*\[*i*\] has been **deleted** from the instance domain.

If *new\_delta*-\>*namelist*\[*i*\] != NULL then the instance identified by *new\_delta*-\>*instlist*\[*i*\] has been **added** to the instance domain.

Because the \`\`delta indom'' is only likely to have short-term relevance to the caller, the *new\_delta*-\>*namelist*\[*i*\] entries that are not NULL will point back into *old*-\>*namelist*\[*j*\] or *new*-\>*namelist*\[*k*\] and so *old* and *new* should not be freed until the caller has finished with *new\_delta*.

## SEE ALSO

[**PMAPI**(3)](/PMAPI/3.md), [**pmaSortInDom**(3)](/pmaSortInDom/3.md) and [**pmaSameInDom**(3)](/pmaSameInDom/3.md).