direction: right

Write: {
  label: "Write\nkey, value"
  shape: rectangle
}
Memtable: {
  label: "Memtable\nin-memory tree\n(sorted)"
  shape: rectangle
}
WAL: {
  label: "WAL\nappend-only log\n(crash recovery)"
  shape: rectangle
}
SSTable: {
  label: "SSTable\nsorted segment\non disk"
  shape: rectangle
}
Compaction: {
  label: "Compaction\nmerge segments,\ndrop old values"
  shape: rectangle
}
Read: {
  label: "Read\nmemtable first,\nthen newest segment"
  shape: rectangle
}

Write -> Memtable
Write -> WAL
Memtable -> SSTable: "flush when\n> threshold"
SSTable -> Compaction
Compaction -> SSTable: "merged\nsegments"
Read -> Memtable
Read -> SSTable