The Cost of TDE and Checksums in PGEE

It's been a while since the last performance check of Transparent Data Encryption (TDE) in Cybertec's PGEE distribution - that was in 2016. Of course, the question is still interesting, so I did some benchmarks.

Since the difference is really small between running without any extras, with data checksums turned on, and with both encryption and checksums turned on, we need to pick a configuration that will stress-test these features the most. So in the spirit of making PostgreSQL deliberately run slow, I went with only 1MB of shared_buffers with a pgbench workload of scale factor 50. The 770MB of database size will easily fit into RAM. However, having such a small buffer cache setting will cause a lot of cache misses with pages re-read from the OS disk cache, checksums checked, and the page decrypted again. To further increase the effect, I ran pgbench --skip-some-updates so the smaller, in-cache-anyway pgbench tables are not touched. Overall, this yields a pretty consistent buffer cache hit rate of only 82.8%.

Here are the PGEE 17.6 tps (transactions per second) numbers averaged over a few 1-minute 3-client pgbench runs for different combinations of data checksums on/off, TDE off, and the various supported key bit lengths:

There is a lot of noise in the individual runtimes before averaging, so the numbers must be viewed with some care (192-bit TDE is certainly not faster with checksums than without), but if we dare to interpret these tiny differences, we can conclude the following:

• The cost of enabling data checksums on this bad-cache-ratio workload is about 0.25 %.
• The cost of enabling both TDE encryption and data checksums on this workload is about 0.5%.

Any workload with a better shared_buffers cache hit rate would see a lower penalty of enabling checksums and TDE than that.