Tendermint Core QA Results v0.34.x

200 Node Testnet

Finding the Saturation Point

The first goal when examining the results of the tests is identifying the saturation point. The saturation point is a setup with a transaction load large enough to prevent the testnet from being stable: the load runner tries to produce slightly more transactions than can be processed by the testnet. The following table summarizes the results for v0.34.x for the different experiments (extracted from file v034_report_tabbed.txt). The X axis of this table is c, the number of connections created by the load runner process to the target node. The Y axis of this table is r, the rate or number of transactions issued per second.

	c=1	c=2	c=4
r=25	2225	4450	8900
r=50	4450	8900	17800
r=100	8900	17800	35600
r=200	17800	35600	38660

The table shows the number of 1024-byte-long transactions that were produced by the load runner and processed by Tendermint Core during the 90 seconds of the experiment’s duration. Each cell in the table refers to an experiment with a particular number of websocket connections (c) to a chosen validator and the number of transactions per second that the load runner tries to produce (r). Note that the overall load the tool attempts to generate is

c \cdot r

. We can see that the saturation point is beyond the diagonal that spans cells

r=200,c=2
r=100,c=4

given that the total number of transactions should be close to the product rate × the number of connections × experiment time. All experiments below the saturation diagonal (r=200,c=4) have in common that the total number of transactions processed is noticeably less than the product

c \cdot r \cdot 89

(89 seconds, since the last batch never gets sent), which is the expected number of transactions when the system is able to handle the load well. With (r=200,c=4), we obtained 38660, whereas the theoretical number of transactions should have been

200 \cdot 4 \cdot 89 = 71200

. At this point, we chose an experiment at the limit of the saturation diagonal in order to further study the performance of this release. The chosen experiment is (r=200,c=2). This is a plot of the CPU load (average over 1 minute, as output by top) of the load runner for (r=200,c=2), where we can see that the load stays close to 0 most of the time.

Examining Latencies

The method described here allows us to plot the latencies of transactions for all experiments.

As we can see, even the experiments beyond the saturation diagonal managed to keep transaction latency stable (i.e., not constantly increasing). Our interpretation is that contention within Tendermint Core was propagated via the websockets to the load runner; hence, the load runner could not produce the target load but a fraction of it. Further examination of the Prometheus data (see below) showed that the mempool contained many transactions at steady state but did not grow much without quickly returning to this steady state. This demonstrates that the Tendermint Core network was able to process transactions at least as quickly as they were submitted to the mempool. Finally, the test script ensured that at the end of an experiment, the mempool was empty so that all transactions submitted to the chain were processed. Finally, the number of points present in the plot appears to be much less than expected given the number of transactions in each experiment, particularly close to or above the saturation diagonal. This is a visual effect of the plot; what appear to be points in the plot are actually potentially huge clusters of points. To corroborate this, we have zoomed in the plot above by setting (carefully chosen) tiny axis intervals. The cluster shown below looks like a single point in the plot above.

The plot of latencies can be used as a baseline to compare with other releases. The following plot summarizes average latencies versus overall throughput across different numbers of WebSocket connections to the node into which transactions are being loaded.

Prometheus Metrics on the Chosen Experiment

As mentioned above, the chosen experiment is r=200,c=2. This section further examines key metrics for this experiment extracted from Prometheus data.

Mempool Size

The mempool size, a count of the number of transactions in the mempool, was shown to be stable and homogeneous at all full nodes. It did not exhibit any unconstrained growth. The plot below shows the evolution over time of the cumulative number of transactions inside all full nodes’ mempools at a given time. The two spikes that can be observed correspond to a period where consensus instances proceeded beyond the initial round at some nodes.

The plot below shows the evolution of the average over all full nodes, which oscillates between 1500 and 2000 outstanding transactions.

The peaks observed coincide with the moments when some nodes proceeded beyond the initial round of consensus (see below).

Peers

The number of peers was stable at all nodes. It was higher for the seed nodes (around 140) than for the rest (between 21 and 74). The fact that non-seed nodes reach more than 50 peers is due to #9548.

Consensus Rounds per Height

Most nodes used only round 0 for most heights, but some nodes needed to advance to round 1 for some heights.

Blocks Produced per Minute, Transactions Processed per Minute

The blocks produced per minute are the slope of this plot.

Over a period of 2 minutes, the height goes from 530 to 569. This results in an average of 19.5 blocks produced per minute. The transactions processed per minute are the slope of this plot.

Over a period of 2 minutes, the total goes from 64525 to 100125 transactions, resulting in 17800 transactions per minute. However, we can see in the plot that all transactions in the load are processed long before the two minutes. If we adjust the time window for when transactions are processed (approx. 105 seconds), we obtain 20343 transactions per minute.

Memory Resident Set Size

Resident Set Size of all monitored processes is plotted below.

The average over all processes oscillates around 1.2 GiB and does not demonstrate unconstrained growth.

CPU Utilization

The best metric from Prometheus to gauge CPU utilization on a Unix machine is load1, as it usually appears in the output of top.

It is contained in most cases below 5, which is generally considered acceptable load.

Test Result

Result: N/A (v0.34.x is the baseline) Date: 2022-10-14 Version: 3ec6e424d6ae4c96867c2dcf8310572156068bb6

Rotating Node Testnet

For this testnet, we will use a load that can safely be considered below the saturation point for the size of this testnet (between 13 and 38 full nodes): c=4,r=800. N.B.: The version of CometBFT used for these tests is affected by #9539. However, the reduced load that reaches the mempools is orthogonal to the functionality we are focusing on here.

Latencies

The plot of all latencies can be seen in the following plot.

We can observe there are some very high latencies toward the end of the test. Upon suspicion that they are duplicate transactions, we examined the latencies raw file and discovered there are more than 100K duplicate transactions. The following plot shows the latencies file where all duplicate transactions have been removed, i.e., only the first occurrence of a duplicate transaction is kept.

This problem, existing in v0.34.x, will need to be addressed, perhaps in the same way we addressed it when running the 200 node test with high loads: increasing the cache_size configuration parameter.

Prometheus Metrics

The set of metrics shown here are fewer than for the 200 node experiment. We are only interested in those for which the catch-up process (blocksync) may have an impact.

Blocks and Transactions per Minute

Just as shown for the 200 node test, the blocks produced per minute are the gradient of this plot.

Over a period of 5229 seconds, the height goes from 2 to 3638. This results in an average of 41 blocks produced per minute. The following plot shows only the heights reported by ephemeral nodes (which are also included in the plot above). Note that the height metric is only shown once the node has switched to consensus, hence the gaps when nodes are killed, wiped out, started from scratch, and catching up.

The transactions processed per minute are the gradient of this plot.

The small lines we see periodically close to y=0 are the transactions that ephemeral nodes start processing when they are caught up. Over a period of 5229 seconds, the total goes from 0 to 387697 transactions, resulting in 4449 transactions per minute. We can see some abrupt changes in the plot’s gradient. This will need to be investigated.