architecture-diagram.gv

digraph G {

  subgraph clusterRequests {
    node [style = filled];
    rank = source;
    "Resource request";
    "Stream request";
    Ack;
  }

  subgraph clusterApplication {
    label = "APP";
    color = purple;
    "Resource controller" [shape = Mdiamond];
    "Changefeed controller" [shape = Mdiamond];
    ChangefeedSource [shape = diamond, style = filled];
    ChangefeedFetcher [shape = diamond, style = filled];
    AckSubscriptionManager [shape = Mdiamond];
    ScratchExpander [shape = Mdiamond];
    { rank = same; ChangefeedSource; ChangefeedFetcher; }
  }
  subgraph clusterDatabase {
    label = "HYDRADB";
    color=blue;
    rank=sink;
    node [shape = box];
    resource;
    change_history_to_expand;
    change_history;
    changefeed;
  }
  "Resource request" -> "Resource controller" [dir = both];
  "Stream request" -> "Changefeed controller";
  Ack -> "Changefeed controller";

  "Changefeed controller" -> ChangefeedSource [label = "creates"];
  "Changefeed controller" -> changefeed [label = "ack"];
  ChangefeedSource -> "Stream request" [label = "HTTP chunked response"];
  ChangefeedSource -> ChangefeedFetcher [dir = both];

  "Resource controller" -> resource [dir = both];
  resource -> change_history_to_expand  [label = "propagate_resource_edit()"];
  ScratchExpander -> change_history_to_expand [label = "claim one ref", dir=both, arrowhead=none];
  ScratchExpander -> change_history [label = "write ref and all related refs"];
  AckSubscriptionManager -> change_history [label = "SELECT MAX(seq);"];
  AckSubscriptionManager -> changefeed [label = "LISTEN 'changefeed_<name>';", dir=both, arrowhead=none, weight=10];
  ChangefeedFetcher -> change_history [label = "SELECT, LIMIT bufsize;", weight=10, dir=both, arrowhead=none];
  AckSubscriptionManager -> ChangefeedFetcher [dir = both];
}