metrics: fix w-amp calculation w/ blob files

[jbowens]

Fix the w-amp calculation to properly account for blob files. We should be including all bytes written to disk in the numerator, and only bytes "in" (flushed in the case of blob files) in the denominator.

Informs #4581.

[cockroach-teamcity]

This change is 

[RaduBerinde]

Reviewable status: 0 of 3 files reviewed, 2 unresolved discussions

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metrics.go line 189 at r1 (raw file):

//	TableBytesFlushed + TableBytesCompacted + BlobBytesFlushed + BlobBytesWritten
//	-----------------------------------------------------------------------------
//	                      TableBytesIn + BlobBytesFlushed

For L0, TableBytesIn is defined as "the bytes written to the WAL.". This would include BlobBytesFlushed, no?

I checked the code and it's updated here:

pebble/compaction.go

Line 1570 in 88e7636

l0Metrics.TableBytesIn += d.mu.mem.queue[i].logSize

I think it's fine to keep the definition as is, but we need to divide only by TableBytesIn here, and we need to update this line to also add BlobBytesFlushed to it:

pebble/compaction.go

Line 1567 in 88e7636

l0Metrics.TableBytesIn = l0Metrics.TableBytesFlushed

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metrics.go line 194 at r1 (raw file):

		return 0
	}
	return float64(m.TableBytesFlushed+m.TableBytesCompacted+m.BlobBytesFlushed+m.BlobBytesWritten) /

[nit] We should rename BlobBytesWritten to BlobBytesCompacted, it is confusing

[jbowens]

Reviewable status: 0 of 5 files reviewed, 1 unresolved discussion (waiting on @RaduBerinde)

---

metrics.go line 189 at r1 (raw file):

Previously, RaduBerinde wrote…

For L0, TableBytesIn is defined as "the bytes written to the WAL.". This would include BlobBytesFlushed, no?

I checked the code and it's updated here:

pebble/compaction.go

Line 1570 in 88e7636

l0Metrics.TableBytesIn += d.mu.mem.queue[i].logSize

I think it's fine to keep the definition as is, but we need to divide only by TableBytesIn here, and we need to update this line to also add BlobBytesFlushed to it:

pebble/compaction.go

Line 1567 in 88e7636

l0Metrics.TableBytesIn = l0Metrics.TableBytesFlushed

Good catch, done

---

metrics.go line 194 at r1 (raw file):

Previously, RaduBerinde wrote…

[nit] We should rename BlobBytesWritten to BlobBytesCompacted, it is confusing

Done.

[RaduBerinde]

Reviewable status: 0 of 5 files reviewed, all discussions resolved

[jbowens]

TFTR!