Network is a major part of a database infrastructure. However, often performance benchmarks are done on a local machine, where a client and a server are collocated – I am guilty myself. This is done to simplify the setup and to exclude one more variable (the networking part), but with this we also miss looking at how network affects performance.

The network is even more important for clustering products like Percona XtraDB Cluster and MySQL Group Replication. Also, we are working on our Percona XtraDB Cluster Operator for Kubernetes and OpenShift, where network performance is critical for overall performance.

In this post, I will look into networking setups. These are simple and trivial, but are a building block towards understanding networking effects for more complex setups.

Setup

I will use two bare-metal servers, connected via a dedicated 10Gb network. I will emulate a 1Gb network by changing the network interface speed with

ethtool -s eth1 speed 1000 duplex full autoneg off

  command.

I will run a simple benchmark:

sysbench oltp_read_only --mysql-ssl=on --mysql-host=172.16.0.1 --tables=20 --table-size=10000000 --mysql-user=sbtest --mysql-password=sbtest --threads=$i --time=300 --report-interval=1 --rand-type=pareto

This is run with the number of threads varied from 1 to 2048. All data fits into memory – innodb_buffer_pool_size is big enough – so the workload is CPU-intensive in memory: there is no IO overhead.

Operating System: Ubuntu 16.04

Benchmark N1. Network bandwidth

In the first experiment I will compare 1Gb network vs 10Gb network.

threads/throughput	1Gb network	10Gb network
1	326.13	394.4
4	1143.36	1544.73
16	2400.19	5647.73
32	2665.61	10256.11
64	2838.47	15762.59
96	2865.22	17626.77
128	2867.46	18525.91
256	2867.47	18529.4
512	2867.27	17901.67
1024	2865.4	16953.76
2048	2761.78	16393.84

 

Obviously the 1Gb network performance is a bottleneck here, and we can improve our results significantly if we move to the 10Gb network.

To see that 1Gb network is bottleneck we can check the network traffic chart in PMM:

We can see we achieved 116MiB/sec (or 928Mb/sec)  in throughput, which is very close to the network bandwidth.

But what we can do if the our network infrastructure is limited to 1Gb?

Benchmark N2. Protocol compression

There is a feature in MySQL protocol whereby you can see the compression for the network exchange between client and server:

--mysql-compression=on

  for sysbench.

Let’s see how it will affect our results.

threads/throughput	1Gb network	1Gb with compression protocol
1	326.13	198.33
4	1143.36	771.59
16	2400.19	2714
32	2665.61	3939.73
64	2838.47	4454.87
96	2865.22	4770.83
128	2867.46	5030.78
256	2867.47	5134.57
512	2867.27	5133.94
1024	2865.4	5129.24
2048	2761.78	5100.46

 

Here is an interesting result. When we use all available network bandwidth, the protocol compression actually helps to improve the result.

threads/throughput	10Gb	10Gb with compression
1	394.4	216.25
4	1544.73	857.93
16	5647.73	3202.2
32	10256.11	5855.03
64	15762.59	8973.23
96	17626.77	9682.44
128	18525.91	10006.91
256	18529.4	9899.97
512	17901.67	9612.34
1024	16953.76	9270.27
2048	16393.84	9123.84

 

But this is not the case with the 10Gb network. The CPU resources needed for compression/decompression are a limiting factor, and with compression the throughput actually only reach half of what we have without compression.

Now let’s talk about protocol encryption, and how using SSL affects our results.

Benchmark N3. Network encryption

threads/throughput	1Gb network	1Gb SSL
1	326.13	295.19
4	1143.36	1070
16	2400.19	2351.81
32	2665.61	2630.53
64	2838.47	2822.34
96	2865.22	2837.04
128	2867.46	2837.21
256	2867.47	2837.12
512	2867.27	2836.28
1024	2865.4	1830.11
2048	2761.78	1019.23

threads/throughput	10Gb	10Gb SSL
1	394.4	359.8
4	1544.73	1417.93
16	5647.73	5235.1
32	10256.11	9131.34
64	15762.59	8248.6
96	17626.77	7801.6
128	18525.91	7107.31
256	18529.4	4726.5
512	17901.67	3067.55
1024	16953.76	1812.83
2048	16393.84	1013.22

 

For the 1Gb network, SSL encryption shows some penalty – about 10% for the single thread – but otherwise we hit the bandwidth limit again. We also see some scalability hit on a high amount of threads, which is more visible in the 10Gb network case.

With 10Gb, the SSL protocol does not scale after 32 threads. Actually, it appears to be a scalability problem in OpenSSL 1.0, which MySQL currently uses.

In our experiments, we saw that OpenSSL 1.1.1 provides much better scalability, but you need to have a special build of MySQL from source code linked to OpenSSL 1.1.1 to achieve this. I don’t show them here, as we do not have production binaries.

Conclusions

1. Network performance and utilization will affect the general application throughput.
2. Check if you are hitting network bandwidth limits
3. Protocol compression can improve the results if you are limited by network bandwidth, but also can make things worse if you are not
4. SSL encryption has some penalty (~10%) with a low amount of threads, but it does not scale for high concurrency workloads.

Let’s talk about MySQL high availability (HA) and synchronous replication once more.

It’s part of a longer series on some high availability reference architecture solutions over geographically distributed areas.

Part 1: Reference Architecture(s) for High Availability Solutions in Geographic Distributed Scenarios: Why Should I Care?

Part 2: MySQL High Availability On-Premises: A Geographically Distributed Scenario

The Problem

A question I often get from customers is: How do I achieve high availability in case if I need to spread my data in different, distant locations? Can I use Percona XtraDB Cluster?

Percona XtraDB Cluster (PXC), mariadb-cluster or MySQL-Galera are very stable and well-known solutions to improve MySQL high availability using an approach based on multi-master data-centric synchronous data replication model. Which means that each data-node composing the cluster MUST see the same data, at a given moment in time.

Information/transactions must be stored and visible synchronously on all the nodes at a given time. This is defined as a tightly coupled database cluster. This level of consistency comes with a price, which is that nodes must physically reside close to each other and cannot be geographically diverse.

This is by design (in all synchronous replication mechanisms). This also has to be clarified over and over throughout the years. Despite that we still see installations that span across geographic locations, including AWS Regions.

We still see some solutions breaking the golden rule of proximity, and trying to break the rules of physics as well. The problem/mistake is not different for solutions based on-premises or in the cloud (for whatever cloud provider).

Recently I had to design a couple of customer solutions based on remote geographic locations. In both cases, the customer was misled by an incorrect understanding of how the synchronous solution works, and from a lack of understanding of the network layer. I decided I need to cover this topic again, as I have done previously in Galera geographic replication and Effective way to check network connection in a geographically distributed environment 

What Happen When I Put Things on the Network?

Well, let’s start with the basics.

While light travels at 300 million meters per second, the propagation of the electric fields or electric signaling is slower than that.

The real speed depends by the medium used to transmit it. But it can be said that the real speed normally spans from 0% to 99% of light-speed (depending on the transmission medium).

This means that in optimal conditions the signal travels at approximately 299.72Km per millisecond, in good/mid condition about half that at 149.86Km per millisecond, and in bad conditions it could be 3Km per millisecond or less.

To help you understand, the distance between Rome (Italy) and Mountain View (California) is about 10,062Km. At light-speed it will take 33.54ms. In good conditions (90% of light-speed) the signal will take 37.26ms to reach Mountain View, and in less optimal conditions it can easily double to 74.53 ms.

Keep in mind this is the electric field propagation speed: optimal conditions with no interruption, re-routing and so on. Reality will bring all the kind of interruptions, repeaters and routing.

All the physics above works as a baseline. On top of this, each human construct adds functionalities, flexibility and (unfortunately) overhead – leading to longer times and slower speeds.

The final speed will be different than the simple propagation of the electric fields. It will include the transmission time of complex signaling using ICMP protocol, or even higher delays with the use of a very complex protocol like TCP/IP, which includes handshaking, package rerouting, re-sending and so on. On top of that, when sending things over the internet, we need to realize that it is very improbable we will be the only user sending data over that physical channel. As such, whatever we have “on the road” will need to face bandwidth limitation, traffic congestion and so on.

I had described the difference between protocols (ICMP – TCP/IP) here, clarifying how the TCP/IP scenario is very different from using different protocols like ICMP, or the theoretical approach.

What it all means is that we cannot trust the theoretical performance. We must move to a more empirical approach. But we must understand the right empirical approach or we will be misled.

An Example

I recently worked on a case where a customer had two data centers (DC) at a distance of approximately 400Km, connected with “fiber channel”. Server1 and Server2 were hosted in the same DC, while Server3 was in the secondary DC.

Their ping, with default dimension, to Server3 was ~3ms. Not bad at all, right?

We decided to perform some serious tests, running multiple sets of tests with netperf for many days collecting data. We also used the data to perform additional fine tuning on the TCP/IP layer AND at the network provider.

The results produced a common (for me) scenario (not so common for them):

 

The red line is the first set of tests BEFORE we optimized. The yellow line is the results after we optimized.

The above graph reports the number of transactions/sec (AVG) we could run against the different dimension of the dataset and changing the destination server. The full roundtrip was calculated.

It is interesting to note that while the absolute numbers were better in the second (yellow) tests, this was true only for a limited dataset dimension. The larger the dataset, the higher the impact. This makes sense if you understand how the TCP/IP stack works (the article I mentioned above explains it).

But what surprised them were the numbers. Keeping aside the extreme cases and focusing instead on the intermediate case, we saw that shifting from a 48k dataset dimension to 512K hugely dropped the performance. The drop for executed transactions was from 2299 to 219 on Server2 (same dc) and from 1472 to 167 Server3 (different DC).

Also, note that Server3 only managed ~35% fewer transactions comparing to Server2 from the start given the latency. Latency moved from a more than decent 2.61ms to 27.39ms for Server2 and 4.27ms to 37.25ms for Server3.

37ms latency is not very high. If that had been the top limit, it would have worked.

But it was not.

In the presence of the optimized channel, with fiber and so on, when the tests were hitting heavy traffic, the congestion was such to compromise the data transmitted. It hit a latency >200ms for Server3. Note those were spikes, but if you are in the presence of a tightly coupled database cluster, those events can become failures in applying the data and can create a lot of instability.

Let me recap a second the situation for Server3:

We had two datacenters.

• The connection between the two was with fiber
• Distance Km ~400, but now we MUST consider the distance to go and come back. This because in case of real communication, we have not only the send, but also the receive packages.
• Theoretical time at light-speed =2.66ms (2 ways)
• Ping = 3.10ms (signal traveling at ~80% of the light speed) as if the signal had traveled ~930Km (full roundtrip 800 Km)
• TCP/IP best at 48K = 4.27ms (~62% light speed) as if the signal had traveled ~1,281km
• TCP/IP best at 512K =37.25ms (~2.6% light speed) as if the signal had traveled ~11,175km

Given the above, we have from ~20%-~40% to ~97% loss from the theoretical transmission rate. Keep in mind that when moving from a simple signal to a more heavy and concurrent transmission, we also have to deal with the bandwidth limitation. This adds additional cost. All in only 400Km distance.

This is not all. Within the 400km we were also dealing with data congestions, and in some cases the tests failed to provide the level of accuracy we required due to transmission failures and too many packages retry.

For comparison, consider Server2 which is in the same DC of Server1. Let see:

• Ping = 0.027ms that is as if the signal had traveled ~11km light-speed
• TCP/IP best at 48K = 2.61ms as if traveled for ~783km
• TCP/IP best at 512K =27.39ms as if traveled for ~8,217km
• We had performance loss, but the congestion issue and accuracy failures did not happen.

You might say, “But this is just a single case, Marco, you cannot generalize from this behavior!”

You would be right IF that were true (but is not).

The fact is, I have done this level of checks many times and in many different environments. On-premises or using the cloud. Actually, in the cloud (AWS), I had even more instability. The behavior stays the same. Please test it yourself (it is not difficult to use netperf). Just do the right tests with RTT and multiple requests (note at the end of the article).

Anyhow, what I know from the tests is that when working INSIDE a DC with some significant overhead due to the TCP/IP stack (and maybe wrong cabling), I do not encounter the same congestion or bandwidth limits I have when dealing with an external DC.

This allows me to have more predictable behavior and tune the cluster accordingly. Tuning that I cannot do to cover the transmission to Server3 because of unpredictable packages behavior and spikes. >200ms is too high and can cause delivery failures.

If we apply the given knowledge to the virtually-synchronous replication we have with Galera (Percona XtraDB Cluster), we can identify that we are hitting the problems well-explained in Jay’s article Is Synchronous Replication right for your app? There, he explains Callaghan’s Law: [In a Galera cluster] a given row can’t be modified more than once per RTT. 

On top of that, when talking of geographical disperse solutions we have the TCP/IP magnifying the effect at writeset transmission/latency level. This causes nodes NOT residing on the same physical contiguous network delay for all the certification-commit phases for an X amount of time.

When X is predictable, it may range between 80% – 3% of the light speed for the given distance. But you can’t predict the transmission-time of a set of data split into several datagrams, then sent on the internet, when using TCP/IP. So we cannot use the X range as a trustable measure.

The effect is unpredictable delay, and this is read as a network issue from Galera. The node can be evicted from the cluster. Which is exactly what happens, and what we experience when dealing with some “BAD” unspecified network issue. This means that whenever we need to use a solution based on tightly coupled database cluster (like PXC), we cannot locate our nodes at a distance that is longer than the largest RTT time of our shortest desired period of commit.

If our application must apply the data in a maximum of 200ms in one of its functions, our min RTT is 2ms and our max RTT is 250ms. We cannot use this solution, period. To be clear, locating a node on another geolocation, and as such use the internet to transmit/receive data, is by default a NO GO given the unpredictability of that network link.

I doubt that nowadays we have many applications that can wait an unpredictable period to commit their data. The only case when having a node geographically distributed is acceptable is if you accept commits happening in undefined periods of time and with possible failures.

What Is the Right Thing To Do?

The right solution is easier than the wrong one, and there are already tools in place to make it work efficiently. Say you need to define your HA solution between the East and West Coast, or between Paris and Frankfurt. First of all, identify the real capacity of your network in each DC. Then build a tightly coupled database cluster in location A and another tightly coupled database cluster in the other location B. Then link them using ASYNCHRONOUS replication.

Finally, use a tool like Replication Manager for Percona XtraDB Cluster to automatically manage asynchronous replication failover between nodes. On top of all of that use a tool like ProxySQL to manage the application requests.

The full architecture is described here.

Conclusions

The myth of using ANY solution based on tightly coupled database cluster on distributed geographic locations is just that: a myth. It is conceptually wrong and practically dangerous. It MIGHT work when you set it up, it MIGHT work when you test it, it MIGHT even work for some time in production.

By definition, it will break, and it will break when it is least convenient. It will break in an unpredictable moment, but because of a predictable reason. You did the wrong thing by following a myth.

Whenever you need to distribute your data over different geographic locations, and you cannot rely on a single physical channel (fiber) to connect the two locations, use asynchronous replication, period!

References

https://github.com/y-trudeau/Mysql-tools/tree/master/PXC

http://www.tusacentral.net/joomla/index.php/mysql-blogs/164-effective-way-to-check-the-network-connection-when-in-need-of-a-geographic-distribution-replication-.html

https://www.percona.com/blog/2013/05/14/is-synchronous-replication-right-for-your-app/

Sample test

#!/bin/bash
test_log=/tmp/results_$(date +'%Y-%m-%d_%H_%M_%S').txt
exec 9>>"$test_log"
exec 2>&9
exec 1>&9
echo "$(date +'%Y-%m-%d_%H_%M_%S')" >&9
for ip in 11 12 13; do
  echo "  ==== Processing server 10.0.0.$ip === "
  for size in 1 48 512 1024 4096;do
    echo " --- PING ---"
    ping -M do -c 5  10.0.0.$ip -s $size
    echo "  ---- Record Size $size ---- "
    netperf -H 10.0.0.$ip -4 -p 3307 -I 95,10 -i 3,3 -j -a 4096 -A 4096  -P 1 -v 2 -l 20 -t TCP_RR -- -b 5 -r ${size}K,48K -s 1M -S 1M
    echo "  ---- ================= ---- ";
  done
   echo "  ==== ----------------- === ";
done

 

In this article, we’ll look at an example of an on-premises, geographically distributed MySQL high availability solution. It’s part of a longer series on some high availability reference architecture solutions over geographically distributed areas.

Part 1: Reference Architecture(s) for High Availability Solutions in Geographic Distributed Scenarios: Why Should I Care?

Percona consulting’s main aim is to identify simple solutions to complex problems. We try to focus on identifying the right tool, a more efficient solution, and what can be done to make our customers’ lives easier. We believe in doing the work once, doing it well and have more time afterward for other aspects of life.

In our journey, we often receive requests for help – some simple, some complicated.  

Scenario

The company “ACME Inc.” is moving its whole business from a monolithic application to a distributed application, split into services. Each different service deals with the requests independently from each other. Some services follow the tightly-bounded transactional model, and others work/answer asynchronously. Each service can access the data storage layer independently.

In this context, ACME Inc. identified the need to distribute the application services over wide geographic regions, focusing on each region achieving scale independently.

The identified regions are:

• North America
• Europe
• China

ACME Inc. is also aware of the fact that different legislation acts on each region. As such, each region requires independent information handling about sales policies, sales campaigns, customers, orders, billing and localized catalogs, but will share the global catalog and some historical aggregated data. While most of the application services will work feeding and reading local distributed caches, the basic data related to the catalog, sales and billing is based on an RDBMS.

Historical data is instead migrated to a “Big Data” platform, and aggregated data is elaborated and push to a DWH solution at HQ. The application components are developed using multiple programming languages, depending on the service.   

The RDBMS identified by ACME Inc. in collaboration with the local authorities was MySQL-oriented. There were several solutions like:

• PostgreSQL
• Oracle DB
• MS SQL server

We excluded closed-source RDBMSs given that some countries imposed a specific audit plugin. This plugin was only available for the mentioned platforms. The cost of parallel development and subsequent maintenance in case of RDBMS diversification was too high. As such all the regions must use the same major RDBMS component.

We excluded PostgreSQL given that compared to the adoption of MySQL, utilization cases were higher and MySQL had a well-defined code producer. Finally, the Business Continuity team of ACME Inc., had defined an ITSC (Information Technology Service Continuity) plan that defined the RPO (Recovery Point Objective), the RTO (Recovery Time Objective) and system redundancy.

That’s it. To fulfill the ITSCP, each region must have the critical system redundantly replicated in the same region, but not on the proximity.

Talking About the Components

This is a not-so-uncommon scenario, and it also presents a lot of complexity if you try to address it with one solution. But let’s analyze it and see how we can simplify the approach while still meeting the needs and requirements of ACME Inc.

When using MySQL-based solutions, the answer to “what should we use?” is use what best fits your business needs. The “nines” availability reference table for the MySQL world (most RDBMSs) can be summarized below:

9 0. 0 0 0 % (36 days) MySQL Replication
9 9. 9 0 0 % (8 hours) Linux Heartbeat with DRBD (Obsolete DRBD)
9 9. 9 0 0 % (8 hours) RHCS with Shared Storage (Active/Passive)
9 9. 9 9 0 % (52 minutes) MHA/Orchestrator with at least three nodes
9 9. 9 9 0 % (52 minutes) DRBD and Replication (Obsolete DRBD)
9 9 .9 9 5 % (26 minutes) Multi-Master (Galera replication) 3 node minimum
9 9. 9 9 9 % (5 minutes) MySQL Cluster

An expert will tell you that it always doesn’t make sense to go for the most “nines” in the list. This because each solution comes with a tradeoff: the more high availability (HA) you get, the higher the complexity of the solution and in managing the solution.

For instance, the approach used in MySQL Cluster (NDB) makes this solution not suitable for generic utilization. It requires proper analysis of the application needs, data utilization and archiving before being selected. It also requires in-depth knowledge to properly manage the cluster, as it is more complex than other similar solutions.

This indirectly makes a solution based on MySQL+Galera replication the one with the highest HA level a better choice, since it is close to the defaults generalized utilizations. 

This is why MySQL+Galera replication has become in the last six years the most used solution for platform looking for very high HA, without the need to diverge from standard MySQL/InnoDB approach. You can read more about Galera replication: http://galeracluster.com/products/ 

Read more about Percona XtraDB Cluster.

There are several distributions implementing Galera replication:

• Codership (Galera software producer/owner): http://galeracluster.com/downloads/#downloads
• *MariaDB: https://mariadb.com/kb/en/library/what-is-mariadb-galera-cluster/
• Percona XtraDB Cluster: https://www.percona.com/downloads/Percona-XtraDB-Cluster-LATEST/

*Note that MariaDB Cluster/Server and all related solutions coming from MariaDB have significantly diverged from the MySQL mainstream. This often means that once migrated to MariaDB; your database will not be compatible with other MySQL solutions. In short, you are locked-in to MariaDB. It is recommended that you carefully evaluate the move to MariaDB before making that move.

Choosing the Components

RDBMS

Our advice is to use Percona XtraDB Cluster (PXC), because at the moment it is one of the most flexible and reliable and compatible solutions. PXC is composed of three main components:

• Percona Server for MySQL
• Percona XtraBackup
• Galera Replication library

The cluster is normally composed of three nodes or more. Each node can be used as a Master, but the preferred and recommended way is to use one node as a Writer and the other as Readers.

Application-wise, accessing the right node can be challenging since this means you need to be aware of which node is the writer, which is the reader, and be able to shift from one to the other if necessary.

Proxy

To simplify this process, it helps to have an additional component that works as a “proxy” connecting the application layer to the desired node(s). The most popular solutions are:

• HAProxy
• ProxySQL

There are several important differences between the two. But in summary, ProxySQL is a Level 7 proxy and is MySQL protocol aware. So, while HAProxy is just passing the connection over as a forward proxy (level 4), ProxySQL is aware of what is going through it and acts as reverse proxy. 

With ProxySQL is possible to decide, based on several parameters, where to send traffic (read/write split and more), what must be stopped, or if we should rewrite an incoming SQL command. A lot of information is available on the ProxySQL website https://github.com/sysown/proxysql/wiki and on the Percona Database Performance Blog .

Backup/Restore

No RDBMS platform is safe without a well-tested procedure for backup and recovery. The Percona XtraDB Cluster package distribution comes with Percona XtraBackup as the default method for node provisioning. A good backup and restore (B/R) policy start from the consideration of ACME’s ITSCP, to have full and incremental backups, perfectly covering the RPO, and a good recovery procedure to keep the recovery time inside RTO whenever possible.

There are several tools that allow you to plan and execute backup/restore procedure, some coming from vendors other than open source and community-oriented. In respect to being a fully open source and community-oriented, we in consulting normally suggest using: https://github.com/dotmanila/pyxbackup.

Pyxbackup is a wrapper around XtraBackup that helps simplify the B/R operations, including the preparation of a full and incremental set. This helps significantly reduce the recovery time.  

Disaster Recovery

Another very important aspect of the ITSC Plan is the capacity of the system to survive to major disasters. The disaster and recovery (DR) solution must be able to act as the main production environment. Therefore, it must be designed and scaled as the main production site in resources. It must be geographically separated, normally hundreds of kilometers or more. It must be completely independent of the main site. It must be as much as possible in sync with the main production site.

While the first three “musts” are easy to understand, the fourth one is often the object of misunderstanding.

The concept of be as much in sync with the production site as possible creates confusion in designing HA solutions with Galera replication involved. The most common misunderstanding is the misuse of the Galera replication layer. Mainly the conceptual confusion between tightly coupled database cluster and loosely coupled database cluster.

Any solution based on Galera replication is a tightly coupled database cluster, because the whole idea is to be data-centric, synchronously distributed and consistent. The price is that this solution cannot be geographically distributed.

Solutions like standard MySQL replication are instead loosely coupled database cluster and they are designed to be asynchronous. Given that, the nodes connected by it are completely independent in processing/apply the transaction, and the solution fits perfectly into ANY geographically distributed replication solution. The price is that data on the receiving front might not be up to date with the one from the source in that specific instant.

The point is that for the DR site the ONLY valid solution is the asynchronous link (loosely coupled database cluster), because by design and requirement the two sites must be separated by a significant number of kilometers. For better understanding about why synchronous replication cannot work in a geographically distributed scenario, see “Misuse of Geographic Node distribution with Galera-based replication“.

In our scenario, the use of Percona XtraDB Cluster helps to create a most robust asynchronous solution. This is because each tightly coupled database cluster, no matter if source or destination, will be seen by the other tightly coupled database cluster as a single entity.

What it means is that we can shift from one node to another inside the two clusters, still confident we will have the same data available and the same asynchronous stream passing from one source to the other.

To ensure this procedure is fully automated, we add to our architecture the last block: replication manager for Percona XtraDB Cluster (https://github.com/y-trudeau/Mysql-tools/tree/master/PXC). RMfP is another open source tool that simplifies and automates failover inside each PXC cluster such that our asynchronous solution doesn’t suffer if the node is currently acting as Master fails.  

How to Link the Components

Summarizing all the different components of our solution:

• Application stack
  • Load balancer
  • Application nodes by service
  • Distributed caching
  • Data access service
• Database stack
  • Data proxy (ProxySQL)
  • RDBMS (Percona XtraDB Cluster)
  • Backup/Restore
    • Xtrabackup
    • Pyxbackup
    • Custom scripts
  • DR
    • Replication Manager for Percona XtraDB Cluster
• Monitoring
  • PMM (not covered here see <link> for detailed information)

 

In the solution above, we have two locations separated by several kilometers. On top of them, the load balancer(s)/DNS resolution redirects the incoming traffic to the active site. Each site hosts a full application stack, and applications connect to local ProxySQL.

ProxySQL has read/write enabled to optimize the platform utilization, and is configured to shift writes from one PXC node to another in case of node failure. Asynchronous replication connects the two locations and transmits data from master to slave.

Note that with this solution, it is possible to have multiple geographically distributed sites.

Backups are taken at each site independently and recovery test is performed. RMfP oversees and modifies the replication channels in the case of a node failure.

Finally, Percona Monitoring and Management (PMM) is in place to perform in-depth monitoring of the whole database platform.

Conclusions

We always look for the most efficient, manageable, user-friendly combination of products, because we believe in providing and supporting the community with simple but efficient solutions. What we have presented here is the most robust and stable high availability solution in the MySQL space (except for MySQL NDB that we have excluded). 

It is conceptualized to provide maximum service continuity, with limited bonding between the platforms/sites. It also is a well-tested solution, that has been adopted and adapted in many different scenarios where performance and real HA are a must. I have preferred to keep this digression at a high level, given the details of the implementation have already been discussed elsewhere (see reference section for more reading).

Still, Percona XtraDB Cluster (as any other solution implementing Galera replication) might not fit the final use. Given that, it is important to understand where it does and doesn’t fit. This article is a good summary with examples: Is Synchronous Replication right for your app?.

Check out the next article on How Not to do MySQL High Availability.

References

https://www.percona.com/blog/2016/06/07/choosing-mysql-high-availability-solutions/

https://dev.mysql.com/doc/mysql-ha-scalability/en/ha-overview.html

https://www.percona.com/blog/2014/11/17/typical-misconceptions-on-galera-for-mysql/

http://galeracluster.com/documentation-webpages/limitations.html

http://tusacentral.net/joomla/index.php/mysql-blogs/170-geographic-replication-and-quorum-calculation-in-mysqlgalera.html

http://tusacentral.net/joomla/index.php/mysql-blogs/167-geographic-replication-with-mysql-and-galera.html

http://tusacentral.net/joomla/index.php/mysql-blogs/164-effective-way-to-check-the-network-connection-when-in-need-of-a-geographic-distribution-replication-.html

http://tusacentral.net/joomla/index.php/mysql-blogs/183-proxysql-percona-cluster-galera-integration.html

https://github.com/sysown/proxysql/wiki

 

It’s 2018. Maybe now is the time to start migrating your network to IPv6, and your database infrastructure is a great place to start. Unfortunately, many legacy applications don’t offer the option to connect to MySQL directly over IPv6 (sometimes even if passing a hostname). We can work around this by using ProxySQL’s IPv6 support which was added in version 1.3. This will allow us to proxy incoming IPv4 connections to IPv6-only database servers.

Note that by default ProxySQL only listens on IPv4. We don’t recommended changing that until this bug is resolved. The bug causes ProxySQL to segfault frequently if listening on IPv6.

In this example I’ll use centos7-pxc57-1 as my database server. It’s running Percona XtraDB Cluster (PXC) 5.7 on CentOS 7,  which is only accessible over IPv6. This is one node of a three node cluster, but l treat this one node as a standalone server for this example.  One node of a synchronous cluster can be thought of as equivalent to the entire cluster, and vice-versa. Using the PXC plugin for ProxySQL to split reads from writes is the subject of a future blog post.

The application server, centos7-app01, would be running the hypothetical legacy application.

Note: We use default passwords throughout this example. You should always change the default passwords.

We have changed the IPv6 address in these examples. Any resemblance to real IPv6 addresses, living or dead, is purely coincidental.

• 2a01:5f8:261:748c::74 is the IPv6 address of the ProxySQL server
• 2a01:5f8:261:748c::71 is the Percona XtraDB node

Step 1: Install ProxySQL for your distribution

Packages are available here but in this case I’m going to use the version provided by the Percona yum repository:

[...]
Installed:
proxysql.x86_64 0:1.4.9-1.1.el7
Complete!

Step 2: Configure ProxySQL to listen on IPv4 TCP port 3306 by editing /etc/proxysql.cnf and starting it

[root@centos7-app1 ~]# vim /etc/proxysql.cnf
[root@centos7-app1 ~]# grep interfaces /etc/proxysql.cnf
interfaces="127.0.0.1:3306"
[root@centos7-app1 ~]# systemctl start proxysql

Step 3: Configure ACLs on the destination database server to allow ProxySQL to connect over IPv6

mysql> GRANT SELECT on sys.* to 'monitor'@'2a01:5f8:261:748c::74' IDENTIFIED BY 'monitor';
Query OK, 0 rows affected, 1 warning (0.25 sec)
mysql> GRANT ALL ON legacyapp.* TO 'legacyappuser'@'2a01:5f8:261:748c::74' IDENTIFIED BY 'super_secure_password';
Query OK, 0 rows affected, 1 warning (0.25 sec)

Step 4: Add the IPv6 address of the destination server to ProxySQL and add users

We need to configure the IPv6 server as a mysql_server inside ProxySQL. We also need to add a user to ProxySQL as it will reuse these credentials when connecting to the backend server. We’ll do this by connecting to the admin interface of ProxySQL on port 6032:

[root@centos7-app1 ~]# mysql -h127.0.0.1 -P6032 -uadmin -padmin
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.
Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.5.30 (ProxySQL Admin Module)
Copyright (c) 2009-2018 Percona LLC and/or its affiliates
Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> INSERT INTO mysql_servers(hostgroup_id,hostname,port) VALUES (1,'2a01:5f8:261:748c::71',3306);
Query OK, 1 row affected (0.00 sec)
mysql> INSERT INTO mysql_users(username, password, default_hostgroup) VALUES ('legacyappuser', 'super_secure_password', 1);
Query OK, 1 row affected (0.00 sec)
mysql> LOAD MYSQL USERS TO RUNTIME;
Query OK, 0 rows affected (0.00 sec)
mysql> SAVE MYSQL USERS TO DISK;
Query OK, 0 rows affected (0.27 sec)
mysql> LOAD MYSQL SERVERS TO RUNTIME;
Query OK, 0 rows affected (0.01 sec)
mysql> SAVE MYSQL SERVERS TO DISK;
Query OK, 0 rows affected (0.30 sec)
mysql> LOAD MYSQL VARIABLES TO RUNTIME;
Query OK, 0 rows affected (0.00 sec)
mysql> SAVE MYSQL VARIABLES TO DISK;
Query OK, 95 rows affected (0.12 sec)

Step 5: Configure your application to connect to ProxySQL over IPv4 on localhost4 (IPv4 localhost)

This is application specific and so not shown here, but I’d configure my application to use localhost4 as this is in /etc/hosts by default and points to 127.0.0.1 and not ::1

Step 6: Verify

As I don’t have the application here, I’ll verify with mysql-client. Remember that ProxySQL is listening on 127.0.0.1 port 3306, so we connect via ProxySQL on IPv4 (the usage of 127.0.0.1 rather than a hostname is just to show this explicitly):

[root@centos7-app1 ~]# mysql -h127.0.0.1 -ulegacyappuser -psuper_secure_password
mysql: [Warning] Using a password on the command line interface can be insecure.
mysql> SELECT host FROM information_schema.processlist WHERE ID=connection_id();
+-----------------------------+
| host                        |
+-----------------------------+
| 2a01:5f8:261:748c::74:57546 |
+-----------------------------+
1 row in set (0.00 sec)
mysql> CREATE TABLE legacyapp.legacy_test_table(id int);
Query OK, 0 rows affected (0.83 sec)

The query above shows the remote host (from MySQL’s point of view) for the current connection. As you can see, MySQL sees this connection established over IPv6. So to recap, we connected to MySQL on an IPv4 IP address (127.0.0.1) and were successfully proxied to a backend IPv6 server.

The post Using ProxySQL to connect to IPv6-only databases over IPv4 appeared first on Percona Database Performance Blog.

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