Debugging high latency in toy cluster

Hi,

I’m evaluating FoundationDB for an upcoming project, and I’m seeing way higher latencies than I would expect on writes.

I’m running a 5 node cluster in a local Kubernetes cluster using Kind. The cluster is using a simple statefulset and no process classes specified. I don’t see any significant CPU usage on any of the processes. I am using GitHub - tigrisdata/fdb-exporter: Expose fdb metrics in Prometheus format to export server side metrics.

I have set up a double memory database, and have created a very simple client app in Go that just generates 2 UUIDs and writes them as key-value. After the write, I read back the key and discard the result.

For reads, I’m getting 1-2ms P50 latency, but for writes, P50 is ~15ms, which is quite a lot higher than I would expect.

I have attempted to look at trace files, and have found some indication that LogPush is taking a long time, but debugging that further or resolving it is beyond me :smile:

Logs:

<Event Severity="10" Time="1711640579.008349" DateTime="2024-03-28T15:42:59Z" Type="CommitAttachID" ID="45da311d97d25f27" To="1c6dfe01d0e3124f" Machine="10.244.0.17:4500" LogGroup="default" Roles="CC,CD,CP,SS" />
<Event Severity="10" Time="1711640579.008349" DateTime="2024-03-28T15:42:59Z" Type="CommitDebug" ID="1c6dfe01d0e3124f" Location="CommitProxyServer.commitBatch.Before" Machine="10.244.0.17:4500" LogGroup="default" Roles="CC,CD,CP,SS" />
<Event Severity="10" Time="1711640579.008349" DateTime="2024-03-28T15:42:59Z" Type="CommitDebug" ID="1c6dfe01d0e3124f" Location="CommitProxyServer.commitBatch.GettingCommitVersion" Machine="10.244.0.17:4500" LogGroup="default" Roles="CC,CD,CP,SS" />
<Event Severity="10" Time="1711640579.008816" DateTime="2024-03-28T15:42:59Z" Type="CommitDebug" ID="1c6dfe01d0e3124f" Location="CommitProxyServer.commitBatch.GotCommitVersion" Machine="10.244.0.17:4500" LogGroup="default" Roles="CC,CD,CP,SS" />
<Event Severity="10" Time="1711640579.009514" DateTime="2024-03-28T15:42:59Z" Type="CommitDebug" ID="1c6dfe01d0e3124f" Location="CommitProxyServer.commitBatch.AfterResolution" Machine="10.244.0.17:4500" LogGroup="default" Roles="CC,CD,CP,SS" />
<Event Severity="10" Time="1711640579.009514" DateTime="2024-03-28T15:42:59Z" Type="CommitDebug" ID="1c6dfe01d0e3124f" Location="CommitProxyServer.commitBatch.ProcessingMutations" Machine="10.244.0.17:4500" LogGroup="default" Roles="CC,CD,CP,SS" />
<Event Severity="10" Time="1711640579.009514" DateTime="2024-03-28T15:42:59Z" Type="CommitDebug" ID="1c6dfe01d0e3124f" Location="CommitProxyServer.commitBatch.ApplyMetadaEffect" Machine="10.244.0.17:4500" LogGroup="default" Roles="CC,CD,CP,SS" />
<Event Severity="10" Time="1711640579.009514" DateTime="2024-03-28T15:42:59Z" Type="CommitDebug" ID="1c6dfe01d0e3124f" Location="CommitProxyServer.commitBatch.ApplyMetadaEffect" Machine="10.244.0.17:4500" LogGroup="default" Roles="CC,CD,CP,SS" />
<Event Severity="10" Time="1711640579.009514" DateTime="2024-03-28T15:42:59Z" Type="CommitDebug" ID="1c6dfe01d0e3124f" Location="CommitProxyServer.commitBatch.ApplyMetadaToCommittedTxn" Machine="10.244.0.17:4500" LogGroup="default" Roles="CC,CD,CP,SS" />
<Event Severity="10" Time="1711640579.009514" DateTime="2024-03-28T15:42:59Z" Type="CommitDebug" ID="1c6dfe01d0e3124f" Location="CommitProxyServer.commitBatch.AssignMutationToSS" Machine="10.244.0.17:4500" LogGroup="default" Roles="CC,CD,CP,SS" />
<Event Severity="10" Time="1711640579.009514" DateTime="2024-03-28T15:42:59Z" Type="CommitDebug" ID="1c6dfe01d0e3124f" Location="CommitProxyServer.commitBatch.AfterStoreCommits" Machine="10.244.0.17:4500" LogGroup="default" Roles="CC,CD,CP,SS" />
<Event Severity="10" Time="1711640579.017510" DateTime="2024-03-28T15:42:59Z" Type="CommitDebug" ID="1c6dfe01d0e3124f" Location="CommitProxyServer.commitBatch.AfterLogPush" Machine="10.244.0.17:4500" LogGroup="default" Roles="CC,CD,CP,SS" />
<Event Severity="10" Time="1711640579.017958" DateTime="2024-03-28T15:42:59Z" Type="CommitDebug" ID="1c6dfe01d0e3124f" Location="CommitProxyServer.commitBatch.AfterReportRawCommittedVersion" Machine="10.244.0.17:4500" LogGroup="default" Roles="CC,CD,CP,SS" />

Cluster status:

[root@fdb-kubernetes-example-0 /]# fdbcli
Using cluster file `/var/fdb/data/fdb.cluster'.

The database is available.

Welcome to the fdbcli. For help, type `help'.
fdb> status

Using cluster file `/var/fdb/data/fdb.cluster'.

Configuration:
  Redundancy mode        - double
  Storage engine         - memory-2
  Coordinators           - 3
  Usable Regions         - 1

Cluster:
  FoundationDB processes - 5
  Zones                  - 5
  Machines               - 5
  Memory availability    - 5.3 GB per process on machine with least available
  Retransmissions rate   - 2 Hz
  Fault Tolerance        - 1 zones
  Server time            - 03/28/24 15:46:46

Data:
  Replication health     - Healthy
  Moving data            - 0.000 GB
  Sum of key-value sizes - 62 MB
  Disk space used        - 829 MB

Operating space:
  Storage server         - 0.9 GB free on most full server
  Log server             - 398.2 GB free on most full server

Workload:
  Read rate              - 161 Hz
  Write rate             - 155 Hz
  Transactions started   - 312 Hz
  Transactions committed - 155 Hz
  Conflict rate          - 0 Hz

Backup and DR:
  Running backups        - 0
  Running DRs            - 0

Client time: 03/28/24 15:46:46

Latency statistics from status json:

"commit_latency_statistics" : {
  "count" : 2756,
  "max" : 0.089341599999999993,
  "mean" : 0.010652,
  "median" : 0.010372900000000001,
  "min" : 0.0037507999999999999,
  "p25" : 0.009155990000000001,
  "p90" : 0.0132411,
  "p95" : 0.014465800000000001,
  "p99" : 0.017585,
  "p99.9" : 0.049426100000000001
},

Hope someone is able to point me in the right direction.

I would expect that the higher write latencies are a result of your kind setup. I don’t have the details of your kind setup, but in the end your cluster probably runs in a VM and those 5 nodes are not different Kubernetes nodes and they will share the same device. So it probably makes more sense to setup an actual minimal Kubernetes cluster where each FDB Pod can get its own disk.

The memory storage engine will also write to disk, even thought the name might implies that everything is in memory. In most cases you want to use the ssd storage engine, or the newer rocked/redwood storage engine, depending on the FDB version that you are testing.

If you already use Prometheus you might want to setup the node exporter and look at the disk metrics for your setup.