Oximeter: add queue depth metric.#10736
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…her. Oximeter sends samples from all collection tasks to a shared database batcher, which then inserts samples into clickhouse. The database batcher uses a bounded queue that drops old samples when adding a new sample would overflow the queue. We currently log a warning when dropping an old sample, but operators would have to proactively check those logs in order to notice data loss via this queue. To make dropped samples more visible, this patches introduces a new oximeter metric that counts the number of dropped samples in the database batcher. Note: if the batcher isn't able to push samples to the database at all, we won't be able to record the new metric! However, we write the new metric at the head of the queue, and dropped sample counts persist for the lifetime of the oximeter agent, so we'll be able to push metrics unless the queue is wildly oversaturated. Part of #10552.
In #10683, we added a metric counting the number of samples evicted from the oximeter collector's database_batcher queue. Operators can use that metric to detect that samples are being lost, but not that samples are potentially about to be lost. In other words, we have to wait for something to go wrong to take action. This patch adds a queue depth metric to the collector as well: a histogram recording the current length of the queue each time we push a new batch of samples onto it. Operators can use this metric to detect when the queue depth is approaching its maximum length. Part of #10552.
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In #10683, we added a metric counting the number of samples evicted from the oximeter collector's database_batcher queue. Operators can use that metric to detect that samples are being lost, but not that samples are potentially about to be lost. In other words, we have to wait for something to go wrong to take action.
This patch adds a queue depth metric to the collector as well: a histogram recording the current length of the queue each time we push a new batch of samples onto it. Operators can use this metric to detect when the queue depth is approaching its maximum length.
Part of #10552.
Note: builds on #10683. Can just review the second commit, or review both commits here and ignore #10683.
And I promise I'm almost done thinking about #10552. This is one of the last papercuts before I'll feel like this is sorted.