Template editor hangs Home Assistant

[to4ko]

The problem

testing templates in editor in 115.0-115.3 very tricky -making mistake in template you are getting hanging system, only container restart via portainer helps. below you can find log at the moment of testing. I think test environment should not lead to system reboot at any case

Environment

• Home Assistant Core release with the issue: 115.3 (same on 115.0 - 115.2)
• Last working Home Assistant Core release (if known): 144.4
• Operating environment (OS/Container/Supervised/Core): Ubuntu Supervised (same on deb10 supervised)
• Integration causing this issue: ??
• Link to integration documentation on our website:

Problem-relevant configuration.yaml

evaluating this kind of templates leads to system hangs (even not able to save config files from IDE addon)

      - service: notify.telegram
        data_template:
          message: >
            {% set time_limit = as_timestamp(now())-4*60*60 %}
            {% set missing = states | selectattr('attributes.last_seen', 'defined') | selectattr('attributes.linkquality', 'defined')| selectattr('attributes.last_seen','<', time_limit*1000 ) | map(attribute='attributes.device.friendlyName') | unique | list  | join(', ') %}
            {% set missing_count = states | selectattr('attributes.last_seen', 'defined') | selectattr('attributes.linkquality', 'defined')| selectattr('attributes.last_seen','<', time_limit*1000 ) | map(attribute='attributes.device.friendlyName') | unique | list | count %}
            {% set z2m_uptime = ((states('sensor.zigbee2mqtt_bridge_uptime')|int) / 3600)|round(1) %}
            {% set z2m2_uptime = ((states('sensor.zigbee2mqtt2_bridge_uptime')|int) / 3600)|round(1) %}

            {% if missing_count >0 %}{{"\U0001f4f6"}} 4 часа (аптайм z2m: {{z2m_uptime}}ч, z2m2: {{z2m2_uptime}}ч) нет ответа от: {{ missing }}
            {%else%}{{"\U00002705"}}Все устройства доступны!{%endif%}

Traceback/Error logs

Additional information

[bdraco]

The system is likely hanging because the template is listening for all state changed events when we can't successfully evaluate a template as optimistically waiting for the template evaluation to be successful. Normally this isn't an issue but it seems like there is something on your instance that is generating more state changed events than the template engine can keep up with which leads to it being overwhelmed.

[bdraco]

I added functionality in #40624 to trap all the jinja2 errors which will prevent listening for all states on error. Regardless, the system should have been able to keep up with that so I suspect you have something else going on as well that might be brought to light with a py-spy recording.

[to4ko]

chief, this templates were working just fine on all my instances up to 114.4. And only in 115 it cause the system to be non-responsive at all (cross tracking from other instances showing that it's offline). Only diff from "general" system that i'm having up to 2500 entities in my system.

this how it looks like from portainer - and it's not dropping down when i do delete the template and press the Reset to Demo ...

it might be hat my templates not the best ones but they were working just fine even on RPI3b+ and this is happening on Xeon system as well as on i3 or celeron...my RPI simple not able to restart container - only power cycle helps...

[bdraco]

chief, this templates were working just fine on all my instances up to 114.4. And only in 115 it cause the system to be non-responsive at all (cross tracking from other instances showing that it's offline).

In 0.114.4 we were not capable of tracking all state changed events from a template so you would not get any listeners when using states | ....

Only diff from "general" system that i'm having up to 2500 entities in my system.

How many state changed events / second does the system fire?

[to4ko]

chief, this templates were working just fine on all my instances up to 114.4. And only in 115 it cause the system to be non-responsive at all (cross tracking from other instances showing that it's offline).

In 0.114.4 we were not capable of tracking all state changed events from a template so you would not get any listeners when using states | ....

But it were giving correct answer all the time without any problems. and adding antity_id we were able to set "update interval"

Only diff from "general" system that i'm having up to 2500 entities in my system.

How many state changed events / second does the system fire?

according to my postgre stats - like 15-20 event per seconds.

additionally once system starts evaluation template shown at the top, connection to addons got lost in couple of minutes - i was installing py-spy in terminal addon and get connection closed message. no any reaction on menu\buttons\triggers whatever. only container restart.

[bdraco]

I'm able to replicate the issue with:

{% for var in range(10000) -%}
  {% for var in range(10000) -%}
    {{ var }}
  {%- endfor %}.
{%- endfor %}

[bdraco]

I can't replicate the issue with the template provided in the example using a system with 1200 states on the busiest system I have. The number of state changes events per second is much much lower than the reference system:

sqlite> select date(time_fired), count(*)/86400.0 from events group by date(time_fired);
2020-09-25|0.662002314814815
2020-09-26|0.821550925925926

[to4ko]

I can't replicate the issue with the template provided in the example using a system with 1200 states on the busiest system I have. The number of state changes events per second is much much lower than the reference system:

sqlite> select date(time_fired), count(*)/86400.0 from events group by date(time_fired);
2020-09-25|0.662002314814815
2020-09-26|0.821550925925926

so what can be done?

[bdraco]

I can't replicate the issue with the template provided in the example using a system with 1200 states on the busiest system I have. The number of state changes events per second is much much lower than the reference system:

sqlite> select date(time_fired), count(*)/86400.0 from events group by date(time_fired);
2020-09-25|0.662002314814815
2020-09-26|0.821550925925926

so what can be done?

At 16.18 state changes per second that is ~1.4 million state changed events fired per day.

That's an impressive amount of state changes.

That means the template needs to check 3.5 billion states per day (in this case its actually 7 billion since its iterated twice).

Listening and iterating all states is never going to be viable on a system with those numbers no matter how much we optimize templates.

The only solution I can come up with is to revert the change that added listeners for all states but that isn't going over very well as other users rely on this.

[to4ko]

I can't replicate the issue with the template provided in the example using a system with 1200 states on the busiest system I have. The number of state changes events per second is much much lower than the reference system:

sqlite> select date(time_fired), count(*)/86400.0 from events group by date(time_fired);
2020-09-25|0.662002314814815
2020-09-26|0.821550925925926

so what can be done?

At 16.18 state changes per second that is ~1.4 million state changed events fired per day.

That's an impressive amount of state changes.

That means the template needs to check 3.5 billion states per day (in this case its actually 7 billion since its iterated twice).

Listening and iterating all states is never going to be viable on a system with those numbers no matter how much we optimize templates.

The only solution I can come up with is to revert the change that added listeners for all states but that isn't going over very well as other users rely on this.

maybe optionally add entity_id back - if it's specified use it (114 style), if not - than new 115 style

[bdraco]

maybe optionally add entity_id back - if it's specified use it (114 style), if not - than new 115 style

The template tracking is used in bayesian sensors, template entities, automation triggers, universal media players, and the websocket api (the case you are reporting). This would handle the template entities case but it doesn't solve the issue you are reporting.

[to4ko]

maybe optionally add entity_id back - if it's specified use it (114 style), if not - than new 115 style

The template tracking is used in bayesian sensors, template entities, automation triggers, universal media players, and the websocket api (the case you are reporting). This would handle the template entities case but it doesn't solve the issue you are reporting.

it will. my system will not hang on template testing. as of now - i need to restart container each time when i have an error. plus - to be honest - do we really need this "feature"? it was working just fine in the past. and not it's enchanted meaning broken.

[bdraco]

chief, this templates were working just fine on all my instances up to 114.4. And only in 115 it cause the system to be non-responsive at all (cross tracking from other instances showing that it's offline).

In 0.114.4 we were not capable of tracking all state changed events from a template so you would not get any listeners when using states | ....

Only diff from "general" system that i'm having up to 2500 entities in my system.

How many state changed events / second does the system fire?

I use similar templates and they were correctly working until update to 0.115. It sounds very strange that "your instance that is generating more state changed events than the template engine can keep up with which leads to it being overwhelmed" while all previous HA versions were really capable to work with such templates. It is definitely because of non-optimized template engine code in 0.115 which is still not ready for release.

I also propose to add two features to templates engine:

1. it should have something like "template calculation timeout" inside and force stop any further calculation (with corresponding error/warning message in log) in case the engine is not capable to complete necessary updates online. It will significantly increase system stability in any case. The system behaviour when any entity can cause its hang up is not correct architectural solution.

jinja doesn't have a timeout capability. Since we have to render templates in async we don't have an easy way of aborting the execution without a signal which may not be safe to do.
pallets/jinja#161

2. HA documentation tells that any standard integration should work with some common parameters such as 'scan_interval' (home-assistant.io/docs/configuration/platform_options). At the moment HA doesn't allow to use scan_interval in template sensor. For some 'heavy' sensors like above mentioned this option could also help to solve the problem. In case 'scan_interval' is not specified the template engine will update template by default rules.

If we implemented that we would end up with multiple template implementations in template entities. This issue isn't about template entities though its about the template editor hanging in developer tools.

[to4ko]

If we implemented that we would end up with multiple template implementations in template entities. This issue isn't about template entities though its about the template editor hanging in developer tools.

but it will became about template templates in general once a user will create this kind of template. dev tool is just on the top of all that

[bdraco]

I'm come back to this once #40272 is reviewed as it will give more flexibility on how we can handle this without breaking state counting.

[bdraco]

Assuming it solves all the cases, disabling the all states listener by default and implementing a flag allow_all_states_listener to turn it on seems a reasonable path forward after we can separate counting from iterating in #40272 as it means we don't end up with two implementations in template entities.

[bdraco]

disabling the all states listener by default and implementing a flag allow_all_states_listener to turn it on seems a reasonable path forward

Instead of creating a new option, called allow_all_states_listener, which serves a single purpose, why not simply restore entity_id and allow it to accept states as a valid value? It would allow for more flexibility than a new, one-trick pony.

Restoring entity_id would require the user to know about the flag in advance instead of trying to figure it out after they already have a performance issue. It also doesn't solve this issue.

[bdraco]

Since allow_all_states_listener doesn't seem to be desired, I'm going to hold off moving forward until we can come up with a solution that accommodates the use cases without implementing two systems and solves the issue submitted here.

[balloob]

Please do not spam this issue with discussion about entity_id being brought back. I've hid these comments. Next occurrence will result in a ban. This is the issue tracker, not for feature requests. The only thing you guys are achieving is that you are harassing someone who is actually trying to solve the problems. That's not something we accept in this community.

[bdraco]

Within the scope of the dev tools we need some type of safety net since users need to be able to safely experiment that covers:

1. Very expensive templates

Example: massive iteration

{% for var in range(10000) -%}
  {% for var in range(10000) -%}
    {{ var }}
  {%- endfor %}
{%- endfor %}

2. Templates that re-fire too frequently

Example: iterate all states on busy systems (with the reference point being 1 million state change events per day or 3.5 billion iterates)

{{ states | list }}

3. We end up with an all listener unexpectedly when we have a template error

Example: any invalid template.

• For 1 this is a single execution run problem where we need a way abort execution of a template that takes more than x seconds. Abort execution of template renders that overwhelm the system #40647

• For 2 the problem is the cumulative expense of execution where a rate limit probably makes sense. Will likely implement rate_limit as described as limit in Template Component: Handling non-deterministic and frequently updating templates architecture#206. Implement template rate limits #40667

• We also need to tell the websocket api to use the rate limit from the dev tools (frontend change and websocket api change)

• For 3 Ensure all jinja2 errors are trapped and displayed in the developer tools #40624 addresses this issue

[Mariusthvdb]

As posted here https://community.home-assistant.io/t/heads-up-upcoming-breaking-change-in-the-template-integration/223715/372?u=mariusthvdb

    {% set ns = namespace(domains=[]) %}

      {% for d in states|groupby('domain') %}

      {% set ns.domains = ns.domains + [d[0]] %}

      {% endfor %}

      {% set list = ns.domains|join('\n') %}

      {{list if list|count < 255 else

        list|replace('input','inp')|truncate(255,true)}}

115 is a bit too anxious to evaluate on state changes... no issues with these templates up to 114.

just to add to the thread here, for reference, thought it might be useful

and yes, only 'ha core restart' will do. The template testing for unavailable in that same thread, made even that impossible forcing to ha host reboot. Won't copy the thread any further

Why was this hidden? It was on the exact issue of this issue tracker my contribution was aimed. A template killing the instance in dev template tools

Please unhide?

[amelchio]

For 2 the problem is the cumulative expense of execution where a rate limit probably makes sense.

Penny had some thoughts on this while working on the new template engine: home-assistant/architecture#206 – maybe it's better to continue the point 2 discussion there.

[bdraco]

For 2 the problem is the cumulative expense of execution where a rate limit probably makes sense.

Penny had some thoughts on this while working on the new template engine: home-assistant/architecture#206 – maybe it's better to continue the point 2 discussion there.

Fantastic 👍 🥇 💯 🚀

This is exactly the help I was looking for 😄 😄 😄

[Petro31]

@bdraco This may be related, I've noticed that listeners are set to all states when using states.domain.object_id with an object_id that is not present on the system (i.e. a typo). Is this intended or a bug?

[bdraco]

@bdraco This may be related, I've noticed that listeners are set to all states when using states.domain.object_id with an object_id that is not present on the system (i.e. a typo). Is this intended or a bug?

@Petro31
That is intended because we don't know if the entity is about to be added. If it really is a typo it doesn't cost much since its storing a dict key/value that which has near O(1) performance and since we will never get a state changed event for an entity that doesn't exist its not really an issue.

[Petro31]

@bdraco This may be related, I've noticed that listeners are set to all states when using states.domain.object_id with an object_id that is not present on the system (i.e. a typo). Is this intended or a bug?

@Petro31
That is intended because we don't know if the entity is about to be added. If it really is a typo it doesn't cost much since its storing a dict key/value that which has near O(1) performance and since we will never get a state changed event for an entity that doesn't exist its not really an issue.

Great, thanks