Meltdown Vulnerability Impact On MariaDB Server

Posted on January 24, 2018 by MariaDB

Recent attacks, dubbed Meltdown and Spectre, have had a significant impact on various data processors and data security. In response, processors require modifications to the operating system; however, those modifications can be expensive and lead to potential slowdown in the applications and services. The following will explore the performance impact of the Meltdown workaround in the Linux kernel specific to MariaDB Server.

Test Environment

All tests were run on our benchmark machine: 2x 8 core Intel Xeon E5 v3 (Haswell) running Ubuntu Server LTS. We compared kernels 4.4.0-104 and 4.4.0-109. 4.4.0-104 is the last Ubuntu kernel in the 4.4.0 line without the KPTI patch. KPTI stands for Kernel Page Tabe Isolation and is meant as a remedy for the Meltdown attack.

The benchmark is sysbench 1.0 OLTP in read-only and read/write mode. The MariaDB Server version used for this benchmark is MariaDB Server 10.2.11 (GA). MariaDB Server was running mostly with defaults. The InnoDB Buffer Pool was configured to large (all reads coming from memory). The durability was for production (flush-log-at-trx-commit=1). Storage in this machine is SSD.

Since the performance often depends on the malloc implementation, a system function that allocates memory for the program, I ran two series of tests. One with the default glibc malloc and a second with tcmalloc (preloaded with the –malloc-lib option for mysqld_safe).

Results

The numbers shown below are queries per second. Note: higher is better.

OLTP read-only

	glibc malloc			tcmalloc
threads	4.4.0	4.4.0 KPTI	change	4.4.0	4.4.0 KPTI	change
1	17111	14894	-12.96%	16091	16039	-0.32%
2	31966	28777	-9.98%	29426	29396	-0.10%
4	56142	53817	-4.14%	54330	56160	+3.37%
8	109148	107049	-1.92%	105223	103910	-1.25%
16	206156	202927	-1.57%	206005	204688	-0.64%
32	279125	259109	-7.17%	290233	278157	-4.16%
64	270800	240219	-11.29%	290560	281810	-3.01%
128	259024	226367	-12.61%	282176	276145	-2.14%
256	262552	232061	-11.61%	284642	277417	-2.54%

Screen Shot 2018-01-24 at 8.51.03 AM.png

The impact of KPTI seems to be much higher at high concurrency. Tcmalloc delivers not only better results, but also the impact of KPTI is somewhat lessened.

OLTP read/write

	glibc malloc			tcmalloc
threads	4.4.0	4.4.0 KPTI	change	4.4.0	4.4.0 KPTI	change
1	4706	4584	-2.59%	4772	4805	+0.69%
2	9407	9283	-1.32%	9620	9515	-1.09%
4	15912	15860	-0.33%	16436	15975	-2.80%
8	30531	29200	-4.36%	30786	32298	+4.91%
16	61954	61102	-1.38%	63526	63651	+0.20%
32	126154	121657	-3.56%	129561	128284	-0.99%
64	192459	180334	-6.30%	198795	195860	-1.48%
128	220700	200473	-9.16%	234564	229417	-2.19%
256	227077	164281	-27.65%	241731	235218	-2.69%

Screen Shot 2018-01-24 at 8.51.21 AM.png

For read/write workload the KPTI impact is even higher at high thread counts. Again tcmalloc seems to deliver better results.

Conclusion

The Meltdown patch in the Linux kernel reduces the performance of MariaDB Server by 5% and, in some cases, more than 10%, depending on workload and concurrency. The performance impact is higher with high concurrency. In that case, it may help to try running MariaDB Server with a preloaded high-concurrency memory allocator like tcmalloc, jemalloc or other allocator of choice.

Additional Resources

There are some reports from third parties about KPTI regression for MySQL or general performance impact from Redhat that are worth reviewing. Their results are in line with what we found.