maria-discuss team mailing list archive

[<Rhys.Campbell@xxxxxxxxxxxx>]

Might be worth having a look at TokuDB https://mariadb.com/kb/en/library/tokudb/

From: Maria-discuss <maria-discuss-bounces+rhys.campbell=swisscom.com@xxxxxxxxxxxxxxxxxxx> On Behalf Of JCA
Sent: 07 October 2019 21:03
To: Kenneth Penza <kpenza@xxxxxxxxx>
Cc: Mailing-List mariadb <maria-discuss@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Maria-discuss] Performance tuning sought for MariaDB



On Mon, Oct 7, 2019 at 12:12 PM Kenneth Penza <kpenza@xxxxxxxxx<mailto:kpenza@xxxxxxxxx>> wrote:
Opening many connections will cause issues, especially if each thread is running a sub-optimal query. Try to decrease the number of connections, one-way can be using message queues.

Tuning the database I/O is important, ensure you are using a separate mount point for /var/lib/mysql and mount it with noatime. Resize the innodb_buffer_pool_size to ensure that it can hold your workload. Subsequently, perform some tests with innodb_flush_method = "O_DIRECT".

From your description, data S is the key which in turn is composed of T and A. Can the data be stripped by the application and T and A stored separately? Maybe use persistent virtual columns and index those instead.

       I don't think I understand. It is not that S is composed of T and A; what I am reading from the FIFO is two items: S and A. T is derived from S and A, together with a timestamp.

Recall that in InnoDB the primary key is a clustered index thus the table is written to disk sorted by column S. Inserts and updates may require moving rows around slowing the SQL statements (high insert/update concurrency will worsen the situation). If column S is the primary key and is large, all other indexes will use the primary key as the prefix, causing indexes to be large increasing the load on the system I/O.

      There is something to what you are saying, for I have a high insert/update concurrency. I will definitely try to understand to details of what you are suggesting.



On Mon, Oct 7, 2019 at 7:13 PM JCA <1.41421@xxxxxxxxx<mailto:1.41421@xxxxxxxxx>> wrote:
Thanks for your feedback. Please see my comments  interspersed below.

On Mon, Oct 7, 2019 at 10:38 AM Guillaume Lefranc <guillaume@xxxxxxxxxxxx<mailto:guillaume@xxxxxxxxxxxx>> wrote:
Hello,

thread-handling=pool-of-threads
max_connections = 1000
table_open_cache = 800
query_cache_type = 0
innodb_buffer_pool_size = 512M
innodb_buffer_pool_instances = 10
innodb_adaptive_hash_index_partitions = 20
innodb_lock_wait_timeout = 5000
No need to use buffer pool instances with only 512M of buffer. you said you have 24GB of RAM - why not increase the buffer size? how big is your table on the disk right now? If you want the best performance it must be hold in the buffer.

It does not seem to be that big - about 101 MB. I used the following command:

 SELECT table_name AS `Table`, round(((data_length + index_length) / 1024 / 1024), 2) `Size (MB)` FROM information_schema.TABLES WHERE table_schema = "<my-db-name>";

I had to look it up.


With this, my application can keep up with the FIFO writer, but - depending on the circumstances - my database can't. As I am writing this, there are over 1300 threads connected to my database; any command that I issue at the mysql CLI takes over one minute to return. I am keeping track on how long each thread takes to complete, and that is of the order of hundreds of seconds - sometimes thousands. Each thread is itself simple, in that it just issues a couple of simple MariaDB commands.  Currently my table consists of 1.6 million entries, and growing - on this basis, I expect that things will get only worse. Each entry,however, will never require more than a couple of hundred bytes of storage. The operations that can be undertaken on entries are insertion, deletion and modification, the latter being straightforward - like e.g. incrementing a counter or replacing a short string.

You are not considering many factors which is
a) limiting the number of concurrent threads - with 1300 threads you are creating concurrency races and locking issues. Try limiting your threads to a factor of the # of cores

   I will. Notice, though, that most of the time most of the cores are idle anyway.

b), you're writing to a disk system. The number of CPU cores won't matter if you saturate the disk. You say nothing about the disk, if it's SSD, HDD etc. Note that HDD's are severely handicapped when it comes to concurrent IO operations.

   It is an HDD. I am sure it will be a factor in making things slower.

c) given the factor above you could maybe try relaxing commit to disk if integrity of the data is not of utmost importance, for example by adding "innodb_flush_log_at_trx_commit = 2" to your config.

     Thanks - I'll try that.

My system has 24 GB of  RAM and 12 cores. Occasionally all the cores are fully busy with MariaDB activity, but most of the time barely one or two are.

d) CPU in a DB system will mostly be used for queries (index scans) and some for reindexing but you're only doing writes, so unless you have dozens of indexes
e) Table design - is your table design efficient ? how many rows per sec are you writing? maybe you could also benefit from hash partitioning or clever data types.

I am a newbie when it comes to interacting with MariaDB - please,  bear with me. I know I must use a single database and a single table. I also know - because of the nature of the data that are being written to the FIFO - that the  probability for two different threads to be operating on the same entry in the table at the same time is negligible - i.e. for all practical purposes, that will not happen.
What I need is advice on how to configure my instance of MariaDB to perform optimally in the scenario above. In particular, I would like for it to make better use of all the cores available - in essence, to parallelize the database operations as much as possible.

f) Congratulations, you have managed to contradict yourself in two sentences.
If your workload isn't parallel by design you will not make use of the available cores. Also, your workload sounds IO-bound to me - there's a strong change the disk is the bottleneck.
g) "I know I must use a single database and a single table." How do you know this if you are a newbie? No offense meant but nost of monolithic design is not the best to leverage performance....

     The data that I have consist of a string S, two string attributes T and A, and an integer attribute D.  String S is what I have to use as a key in order to insert/delete/modify entries. Can this be advantageously be stored across several tables?  The S strings have nothing in common, beyond the attributes that I mentioned. As for the parallelism, the essence is what I pointed out - namely, that no two threads will work on the same entry (as accessed by S) at the same time.  They can of course be adding new entries, or deleting existing ones, at the same time, with the proviso that the insertion operations will always be for different values of S, and analogously for the deletion operations. I am indeed open to suggestions about a better design.

-GL
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