I should add that this isn’t the first time this has happened, but it is the first time since I reduced the allocation of RAM for PostgreSQL in the configuration file. I swore that that was the problem, but I guess not. It’s been almost a full week without any usage spikes or service interruptions of this kind, but all of a sudden, my RAM and CPU are maxing out again at regular intervals. When this occurs, the instance is unreachable until the issue resolves itself, which seemingly takes 5-10 minutes.
The usage spikes only started today out of a seven-day graph; they are far above my idle usage.
I thought the issue was something to do with Lemmy periodically fetching some sort of remote data and slamming the database, which is why I reduced the RAM allocation for PostgreSQL to 1.5 GB instead of the full 2 GB. As you can see in the above graph, my idle resource utilization is really low. Since it’s probably cut off from the image, I’ll add that my disk utilization is currently 25-30%. Everything seemed to be in order for basically an entire week, but this problem showed up again.
Does anyone know what is causing this? Clearly, something is happening that is loading the server more than usual.
Here’s an update. I set up atop on my VPS and waited until the issue occurred again. Here’s the atop log from the event.
ATOP - ip-172-31-7-27 2023/07/22 18:40:02 ----------------- 10m0s elapsed
PRC | sys 9m49s | user 12.66s | #proc 134 | #zombie 0 | #exit 3 |
CPU | sys 99% | user 0% | irq 0% | idle 0% | wait 0% |
MEM | tot 957.1M | free 49.8M | buff 0.1M | slab 95.1M | numnode 1 |
SWP | tot 0.0M | free 0.0M | swcac 0.0M | vmcom 2.4G | vmlim 478.6M |
PAG | numamig 0 | migrate 0 | swin 0 | swout 0 | oomkill 0 |
PSI | cpusome 63% | memsome 99% | memfull 88% | iosome 99% | iofull 0% |
DSK | xvda | busy 100% | read 461505 | write 171 | avio 1.30 ms |
DSK | xvda1 | busy 100% | read 461505 | write 171 | avio 1.30 ms |
NET | transport | tcpi 2004 | tcpo 1477 | udpi 9 | udpo 11 |
NET | network | ipi 2035 | ipo 1521 | ipfrw 20 | deliv 2015 |
NET | eth0 ---- | pcki 2028 | pcko 1500 | si 4 Kbps | so 1 Kbps |
PID SYSCPU USRCPU VGROW RGROW RDDSK WRDSK CPU CMD
41 5m17s 0.00s 0B 0B 0B 0B 53% kswapd0
1 21.87s 0.00s 0B -80.0K 1.2G 0B 4% systemd
21681 20.28s 0.00s 0B 4.0K 4.2G 0B 3% lemmy
435 18.00s 0.00s 0B 392.0K 163.1M 0B 3% snapd
21576 17.20s 0.00s 0B 0B 4.2G 0B 3% pict-rs
The culprit seems to be kswapd0 trying to move memory to swap space, although there is no swap space.
I set memory swappiness to 0 on the system for now, I’ll check if that makes a difference.
I had the same thing happen. Max CPU usage, couldn’t even ssh in to fix it and had to reboot from aws console. Logs don’t show anything unusual apart from postgres restarting 30 minutes into the spike, possibly from being killed by the system.
You say yours solved itself in 10 minutes, mine didn’t seem to stop after 2 hours, so I reeboted. It could be that my vps is just 1 CPU, 1 GB RAM, so it took longer doing whatever it was doing.
Now I set up RAM and CPU limits following this question, and an alert so I can hopefully ssh in and figure out what’s happening when it’s happening.
Any suggestions on what I should be looking at if I manage to get into the system?
I’ll save this to look at later, but I did use PGTune to set my total RAM allocation for PostgreSQL to be 1.5GB instead of 2. I thought this solved the problem initially, but the problem is back and my config is still at 1.5GB (set in MB to something like 1536 MB, to avoid confusion).
I’m having similar issues with my instance where I’m the only one on it. I allocated more RAM to it now to see if it does anything.
I did that a while ago, and unfortunately, it didn’t really help. I don’t think it’s an issue of RAM, but rather a daemon or something periodically going nuclear with resource utilization. A configuration issue, perhaps?
Sounds more like it, yes. I’ll keep an eye on it.
Maybe we should create a post in the support community?
You can if you want. Reply here with the link if you do (or mention me if that’s a thing on Lemmy).
Oh, and for completeness:
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We’ve deleted the vast majority of the spam bots that spammed our instance, are currently on closed registration with applications, and have had no anomalous activity since.
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Our server is essentially always at 50% memory (1GB/2GB), 10% CPU (2 vCPUs), and 30% disk (15-20GB/60GB) until a spike. Disk utilization does not change during a spike.
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Our instance is relatively quiet, and we probably have no more than ten truly active users at this point. We have a potential uptick in membership, but this is still relatively slow and negligible.
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This issue has happened before, but I assumed it was fixed when I changed the PostgreSQL configuration to utilize less RAM. This is still the longest lead-up time before the spikes started.
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When the spike resolves itself, the instance works as expected. The issues with service interruptions seems to stem from a drastic increase in resource utilization, which could be caused by some software component that I’m not aware of. I used the Ansible install for Lemmy, and have only modified certain configuration files as required. For the most part, I’ve only added a higher max_client_body_size in the nginx configs for larger images, and have added settings for an SMTP relay to the main config.hjson file. The spikes occured before these changes, which leads me to believe that they are caused by something I have not yet explored.
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These issues occured on both 0.17.4 and 0.18.0, which seems to indicate it’s not a new issue stemming from a recent source code change.
Depending on your timezone, it is possibly a peak in traffic from the US, an overlap of July 4th, Reddit userbase jumping in, and the recent surge on shitposting about…sigh… beans.
