ui: transaction fingerprints page updates data sporadically, ignores custom time interval

[ericharmeling]

The Transaction Fingerprints overview page updates data sporadically, with no regard for the time interval. Something is broken in the table row population.

For example, the Execution Count increments at an impossible rate, while the same stat on the Statements Page remains the same:

https://www.loom.com/share/b331d10e58364848b2908c1dd49d8a6f

This behavior is the same, even when the time interval is fixed (i.e., there should be no change in data with a fixed start and end time).

This issue is present in both CC console and DB console.

Jira issue: CRDB-23991

[ericharmeling]

This issue encompasses #68375.

In addition to execution count, the following column values are affected:

• Transaction Time
• Contention Time
• CPU Time
• Max Memory

[xinhaoz]

I took a quick look. It's because in the render method for the txns table section of the page, we are aggregating the txn stats. That sounds fine, but in the mergeTransactionStats method which is used to perform the aggregation grouping on txnFIngerprintID, we take a shallow copy of the first txn in the txns data array to use as our base txn that we return.
So we proceed to inherit + mutate the stats_data of the first txn, which contains the stats like exec count in one field, and other things like txn fingerprint id, app etc. Then we set the stats field of stats_data to the aggregated result of the stats. This means for every re-render, the base txn stats we're using is that of the previous re-render, explaining the incrementing stats.
An easy backportable fix is just to not mutate the stats_data object of the first txn, just create a new obj:

const mergeTransactionStats = function (txns: Transaction[]): Transaction {
  if (txns.length === 0) {
    return null;
  }
  const txn = { ...txns[0], stats_data: { ...txns[0]?.stats_data } }; // Copy the stats_data object explicitly here.
  txn.stats_data.stats = combineTransactionStats(
    txns.map(t => t.stats_data.stats),
  );
  return txn;
};

[xinhaoz]

As an aside, the txns page needs some serious cleanup. It's gotten so messy to the point we can't even catch when we're mutating props we shouldn't be 😬

[xinhaoz]

I spoke to Eric and since I had a fix on my branch I took over issuing the PR for this. Kudos to him for narrowing it down to the bug happening in aggregation process though.