Home - News ( United States | United Kingdom | Italy | Germany ) - Football scores

Showing content from https://github.com/hashicorp/terraform/issues/26355 below:

Performance issues when referencing high cardinality resources · Issue #26355 · hashicorp/terraform · GitHub

Terraform needs to lookup resource as complete objects containing all instances in order to be able to index them in expressions. When the number of instances is large, this can make expression evaluation take considerably longer.

locals {
    users = yamldecode(file("../users.yaml"))
}

resource "null_resource" "user" {
    for_each = local.users

    triggers = {
        name = each.key
        groups = join(",", each.value)
    }
}

resource "null_resource" "user_group" {
    for_each = local.users

    triggers = {
        name = null_resource.user[each.key].triggers.name
        groups = join(",", each.value)
    }
}

This issue seems to be exacerbated to an extreme degree by the use of for_each.

@eriksw Thanks for detailed notes and the test case!
I've encountered similar issue while trying to create a large number of users (~1k) in AWS - after some experiments I ended up with another test case demonstrating performance issue with certain usage of for_each - https://github.com/mlosev/tf-for_each-performance-test

The issue manifests for both Terraform 0.12.29 and 0.13.0 - it takes Terraform an order of magnitude longer (i.e. 10x+) to plan "slow" configuration versus "fast" configuration for the same number of users and groups (~1000) and empty local state (i.e. Terraform wants to create all resources)
The key difference between configuration is

--- users-0.13-fast/main.tf     2020-08-26 11:06:16.000000000 +0100
+++ users-0.13-slow/main.tf     2020-08-26 11:06:26.000000000 +0100
@@ -15,7 +15,7 @@
     for_each = local.users
 
     triggers = {
-        name = each.key
+        name = null_resource.user[each.key].triggers.name
         groups = join(",", each.value)
     }
 }

On my laptop, the difference in plan time is as follows:

• "slow" configuration

Plan: 2100 to add, 0 to change, 0 to destroy.

------------------------------------------------------------------------

      300.20 real       467.68 user        19.38 sys

• "fast" configuration

Plan: 2100 to add, 0 to change, 0 to destroy.

------------------------------------------------------------------------

        2.71 real         7.77 user         1.66 sys

This is quite unexpected behaviour for Terraform, especially considering that there are no API calls involved with null_resource in this case...

PS. I also tried -parallelism=100 (just in case) for "slow" configuration, and it didn't change anything time-wise.

Originally posted by @mlosev in #18981 (comment)

eriksw, srinathrangaramanujam, horjulf, mhvelplund, kstormp and 41 morezeqk and benoittoulme

RetroSearch is an open source project built by @garambo | Open a GitHub Issue

Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo

HTML: 3.2 | Encoding: UTF-8 | Version: 0.7.4