db: add ingest-time splitting of ssts into virtual ones

Currently, if we identify boundary overlap in a level
during ingest target level calculation, but no data overlap,
we are forced to find a target level above the file we saw
the overlap with (if we can't fall below it, such as if the
existing file is in L6, which happens commonly).

This change takes advantage of virtual sstables to split
existing sstables into two virtual sstables when an ingested
sstable would be able to go into the same level had the sstables
been split that way to begin with. Doing this split reduces a
lot of write-amp as it avoids us from having to compact the
newly-ingested sstable with the sstable it boundary-overlapped with.

Biggest part of #1683. First commit is #2538, which this shares
a lot of logic with (mostly just the excise function).

compaction.go

@@ -1880,15 +1880,27 @@ func (d *DB) runIngestFlush(c *compaction) (*manifest.VersionEdit, error) {
 	ve := &versionEdit{}
 	var level int
 	var err error
+	var fileToSplit *fileMetadata
+	var ingestSplitFiles []ingestSplitFile
 	for _, file := range c.flushing[0].flushable.(*ingestedFlushable).files {
-		level, err = ingestTargetLevel(
+		suggestSplit := d.opts.Experimental.IngestSplit != nil && d.opts.Experimental.IngestSplit() &&
+			d.FormatMajorVersion() >= ExperimentalFormatVirtualSSTables
+		level, fileToSplit, err = ingestTargetLevel(
 			d.newIters, d.tableNewRangeKeyIter, iterOpts, d.cmp,
 			c.version, baseLevel, d.mu.compact.inProgress, file.FileMetadata,
+			suggestSplit,
 		)
 		if err != nil {
 			return nil, err
 		}
 		ve.NewFiles = append(ve.NewFiles, newFileEntry{Level: level, Meta: file.FileMetadata})
+		if fileToSplit != nil {
+			ingestSplitFiles = append(ingestSplitFiles, ingestSplitFile{
+				ingestFile: file.FileMetadata,
+				splitFile:  fileToSplit,
+				level:      level,
+			})
+		}
 		levelMetrics := c.metrics[level]
 		if levelMetrics == nil {
 			levelMetrics = &LevelMetrics{}
@@ -1900,6 +1912,28 @@ func (d *DB) runIngestFlush(c *compaction) (*manifest.VersionEdit, error) {
 		levelMetrics.TablesIngested++
 	}
 
+	updateLevelMetricsOnExcise := func(m *fileMetadata, level int, added []newFileEntry) {
+		levelMetrics := c.metrics[level]
+		if levelMetrics == nil {
+			levelMetrics = &LevelMetrics{}
+			c.metrics[level] = levelMetrics
+		}
+		levelMetrics.NumFiles--
+		levelMetrics.Size -= int64(m.Size)
+		for i := range added {
+			levelMetrics.NumFiles++
+			levelMetrics.Size += int64(added[i].Meta.Size)
+		}
+	}
+
+	if len(ingestSplitFiles) > 0 {
+		ve.DeletedFiles = make(map[manifest.DeletedFileEntry]*manifest.FileMetadata)
+		replacedFiles := make(map[base.FileNum][]newFileEntry)
+		if err := d.ingestSplit(ve, updateLevelMetricsOnExcise, ingestSplitFiles, KeyRange{}, replacedFiles); err != nil {
+			return nil, err
+		}
+	}
+
 	return ve, nil
 }
 
@@ -2069,6 +2103,24 @@ func (d *DB) flush1() (bytesFlushed uint64, err error) {
 					metrics.BytesIn += d.mu.mem.queue[i].logSize
 				}
 			}
+		} else if len(ve.DeletedFiles) > 0 {
+			// c.kind == compactionKindIngestedFlushable && we have deleted files due
+			// to ingest-time splits.
+			//
+			// Iterate through all other compactions, and check if their inputs have
+			// been replaced due to an ingest-time split. In that case, cancel the
+			// compaction.
+			for c2 := range d.mu.compact.inProgress {
+				for i := range c2.inputs {
+					iter := c2.inputs[i].files.Iter()
+					for f := iter.First(); f != nil; f = iter.Next() {
+						if _, ok := ve.DeletedFiles[deletedFileEntry{FileNum: f.FileNum, Level: c2.inputs[i].level}]; ok {
+							c2.cancel.Store(true)
+							break
+						}
+					}
+				}
+			}
 		}
 		err = d.mu.versions.logAndApply(jobID, ve, c.metrics, false, /* forceRotation */
 			func() []compactionInfo { return d.getInProgressCompactionInfoLocked(c) })

data_test.go

@@ -1354,8 +1354,9 @@ func runForceIngestCmd(td *datadriven.TestData, d *DB) error {
 		int,
 		map[*compaction]struct{},
 		*fileMetadata,
-	) (int, error) {
-		return level, nil
+		bool,
+	) (int, *fileMetadata, error) {
+		return level, nil, nil
 	}, nil /* shared */, KeyRange{}, nil /* external */)
 	return err
 }