I have wordpress website running in a VPS server and is handling about 150 mysql queries / second.
Ocassionaly when we notice a spike in traffic to about 200 mysql queries a second the https requests to the site is extremely slow.
The site loads decently with http but with https it takes 20+ seconds.
Gradually over a period of an hour after the spike, the load times get better and then it gets back to normal again.
There server load and memory looks fine. There is only a spike in mysql queries, firewall traffic and eth0 requests. There are no mysql slow queries
Any help would be appreciated.
Thank You
I think your answer is in "disk latency" and "disk utilization" charts.
MySQL works well under small loads, when it can cache all data it needs. But when your results or queries get too big, or you request too many of them, it will start doing many disk I/O operations. This enables you to handle huge loads and very big data, but in the moment you exceed your MySQL allocated memory, you will need to read and write everything to disk.
This would not be so bad if you ran on a local SSD drive. But from the device name I see that you are running on an EBS volume, which is not a real hard drive. It is networked drive, so all the traffic overloads your network connection.
You have several options:
1.) install mysqltuner, let the server operate for some time and then run it and see what it suggest. My guess is, that it will suggest you to increase your MySQL memory pool, decrease number of parallel connections or restructure your queries.
2.) use EC2 instance type with actual local storage (e.g. m3 or r3) and write to local SSD. You can do RAID on several SSD drives to make it even faster.
3.) use EBS optimized instance (dedicated EBS network bandwidth) and correct volume type (some EBS volume types have I/O credits, similar to CPU credits for t-type instances, and when you run of those, your operations will slow down to crawl).
Related
I’m trying to determine a MySQL / Web server bottleneck.
I have three servers. A Web server running Nginx, a remote MySQL server with my Wordpress DB and another remote MySQL server storing our data.
The bottleneck I’m trying to find is between my second MySQL server storing our data and my Web server.
We have a page that has three DataTables on it (three separate queries). It’s loading very slowly, if it does all. Occasionally I’ll get a gateway time out error.
I don’t think the queries themselves are the issue. From DataGrip all three average between 200-500ms. Currently the queries aren’t indexed as I’ve been told the plugin cannot take advantage of indexes, but I might try anyways.
Hardware and Setup:
My MySQL server is an AWS R6G.Large, 2 cores and 16gb ram, SSD of 150 IOPS and 128 MB throughput. innodb_page_size is 32, buffer_pool_size is 11000M, innodb_buffer_pool_instances is 10 and innodb_log_file_size is 1G
Web server is an AWS C6G.Xlarge, 4 cores and 8gb ram, SSD of 150 IOPS and 128 MB throughput. Uses FPM and Opcache.
I’ve tried monitoring using TOP on both servers, but to be honest I’m not sure I have knowledge to properly utilize the information.
I’d really like to determine if it’s hardware or software, somehow, and if it’s hardware is there a way to isolate? I have no problem increasing hardware if that’s actually the problem.
I’m not sure if this is allowed on Stack, but I figure it might be easier to know what’s going on if I record my screen with TOP running on both servers. I added a video to my public Google Drive. The video has both my MySQL server (on the top) and Web server (Nginx, on the bottom). What I did was load the page (3sec mark in video) and recorded the outcome. The video is 1:05, which how long it took for the last table to appear. The video was recorded while my site was in maintenance, so no other IP / traffic could reach either server.
My google drive link:
https://drive.google.com/drive/folders/1NtdE1Z4875i1Xx2Wy2EXGgknt9yuY1IN?usp=sharing
Hopefully someone can help.
Aimee
I have been working on the server migration of a legacy ecommerce application using PHP 5.6.
The switch involved two Dedicated 32 servers from Linode.
One server is for NginX + PHP and the other is for MySQL only.
The legacy application leverages memcached.
After the switch, I can see a heavy internal traffic caused due to private inbound and outbound connections.
So far this element didn't cause any problem on performance.
However, I was under the impression that the queries would be cached on the local machine, and not on the remote.
Because if the query is cached on the remote host, it sill has to transmit the result set over the private network, instead of retrieving from RAM or the local SSD.
Am I assuming this wrong?
It may be that I am missing the point where the private inbound traffic is more beneficial for overall performance when compared to a local cache.
MySQL has a feature called the Query Cache, but this caches query result sets in the mysqld server process, not on the client. If you run the exact same query again after the result has been cached in the Query Cache, it will copy the result from the Query Cache and avoid the cost of running the query again. But this will not avoid the time to transfer the result across the network from mysqld to your PHP application.
Also keep in mind that the MySQL Query Cache is being deprecated and retired.
Alternatively, your application may store data from query results in memcached, but typically this would be done by the application code (I know there are UDF's to read and write memcached from MySQL triggers, but this is a bad idea).
If your memcached service is not on the same host as your PHP code, it would result in network transfer twice: Once when querying the data from MySQL the first time, then again transferring the data into memcached, then later every time you fetch the cached data out of memcached.
PHP also has some features to do in-memory caching, such as APCu. I don't have any experience with this, and it's not clear from a brief scan of the documentation where it stores cached data.
PHP is designed to be a "shared nothing" language. Every PHP request has its own data, and data doesn't normally last until the next request. This is why a cache is typically not kept in PHP memory. Applications rely on either memcached or the database itself, because those will hold data longer than a single PHP request.
If you have a fast enough network, it shouldn't be a high cost to fetch items out of a cache over a network. The performance architects at a past job of mine developed this wisdom:
"Remote memory is faster than local storage."
They meant that if the data is in RAM on a server, then reading it from RAM even with the additional overhead of transferring it across a network is usually better than reading the data from persistent (disk) storage on the local host.
I have started using AWS RDS MYSQL for my use-case.
I am using RDS to store the user uploaded server information from a website.
I have tested uploading 1 file with 500 records; took 20 seconds. Again for testing, I have uploaded 9 files simultaneously with a total of 500 records; took 55 seconds.
I don't know what is the possible reason for this? I am using db.t3.large instance.
Which RDS metric do I need to look after or which Performance Insights metrics?
Is this the issue due to lesser baseline I/O performance of the gp2 volume?
Check the following metrics:
Write IOPS (Count/Second)
Write Latency (Milliseconds)
Network Receive Throughput
Are you running the operation over the internet or within the VPC? There should be some network latency if you are using the internet.
We have two MySQL RDS instances (Master and read replica). As usual we write to the master and read from the slave.
Master server works fine, but we observed that slave server becomes unresponsive time to time.
Observations:
Monitoring Graphs
CPU utilization drops down to 0
Increase in number of connections
Write IOPS, read IOPS, queue depth, write throughput, write latency and read latency drop to 0.
This can be resolved with a restart, but we are interested in finding the root cause. Basically when this happens, we can still log in to mysql prompt, but we can't execute any queries. AWS console shows instance as healthy, no errors are shown.
According to the graphs, there is no any abnormal activity or increase in resource utilization just before this happens. Everything looks normal.
(Small climbs in the attached graphs are normal. Those are in line with the business pattern. Historically instance survived against larger mountains)
Please let me know if you happen to come across such a situation.
Thanks.
Note:
Instance Information
db.m4.xlarge
IOPS 2000
Size 50G
Basically, instance is being under utilized when the issue happens
Note:
If we wait without restarting the instance, it gets restarted automatically with following error.
MySQL restart initiated to address MySQL induced log backup issues. Note that as part of this resulution, a DB Snapshot will be performed after MySQL completes restarting.
Is it normal for mysql to be slow when connecting to a remote host or should it have the same performance as connecting to a local host?
I noticed a small performance difference, when I tried to connect to a remote host, so I'm wondering if that's normal?
Assuming that the remote machine is equal in terms of processing power as your local machine, then the primary difference in speed should be network latency - the round trip time for a network traffic. If you are sending huge amounts of data (e.g., reading or writing large BLOBs), then the network bandwidth can come into play as well and "slow" things down. But in general, the round trip cost is often the biggest factor. If you are executing a large number of "small" queries, this cost difference can be fairly significant when comparing a local connection to a remote connection.
Out of curiosity, I just now ran a test that I had already built that simply runs a bunch of update queries. This is not using MySQL but another client/server DBMS. Thus the results would likely be different, but the idea is the same and I would imagine the relative differences would not be significantly different.
Local host (using IPC comm): 5.3 seconds
Remote host (UDP comm): 20.2 seconds
This involved about 50,000 operations. The remote host was 2 hops away on the LAN with (if I measured it correctly) a round trip latency of approximately 0.25 ms for a packet with a 1 byte payload.
It depends entirely on the network connection between the program and the MySQL database server. A slow network will make the database appear slow.
I'd expect a "small performance difference" (as you described it) to be normal for a remote connection.
By default the MySQL server will perform a reverse DNS lookup the first time a client connects to it. It then stores this in its cache. This can potentially give a performance hit depending on the speed of the reverse DNS resolution.
It can depend on how many MySQL queries you're doing: Slow MySQL Remote Connection
You can optimize your code by converting many small queries into larger ones.