feat: Take into account number of databases in an instance

Instances configured with <1000 PUs only support 10 DBs per 100 PUs
so clamp the minimum size to the relevant number of PUs

Fixes cloudspannerecosystem#286

src/autoscaler-common/types.js

@@ -25,6 +25,7 @@ const AutoscalerUnits = {
  *    currentSize: number,
  *    regional: boolean,
  *    currentNodes: number,
+ *    numDatabases: number,
  *  }} SpannerMetadata
  */
 

src/poller/poller-core/index.js

@@ -272,8 +272,13 @@ async function getSpannerMetadata(projectId, spannerInstanceId, units) {
 
   try {
     const spannerInstance = spanner.instance(spannerInstanceId);
-    const data = await spannerInstance.getMetadata();
-    const metadata = data[0];
+
+    const results = await Promise.all([
+      spannerInstance.getDatabases(),
+      spannerInstance.getMetadata(),
+    ]);
+    const numDatabases = results[0][0].length;
+    const metadata = results[1][0];
     logger.debug({
       message: `DisplayName:     ${metadata['displayName']}`,
       projectId: projectId,
@@ -294,6 +299,11 @@ async function getSpannerMetadata(projectId, spannerInstanceId, units) {
       projectId: projectId,
       instanceId: spannerInstanceId,
     });
+    logger.debug({
+      message: `numDatabases:    ${numDatabases}`,
+      projectId: projectId,
+      instanceId: spannerInstanceId,
+    });
 
     /** @type {SpannerMetadata}     */
     const spannerMetadata = {
@@ -304,6 +314,7 @@ async function getSpannerMetadata(projectId, spannerInstanceId, units) {
       regional: !!metadata['config']?.split('/')?.pop()?.startsWith('regional'),
       // DEPRECATED
       currentNodes: assertDefined(metadata['nodeCount']),
+      numDatabases: numDatabases,
     };
     return spannerMetadata;
   } finally {

src/scaler/README.md

@@ -130,6 +130,7 @@ The following is an example:
       }
    ],
    "currentSize":100,
+   "numDatabases": 10,
    "regional":true
 }
 ```

src/scaler/scaler-core/scaling-methods/base.js

@@ -37,7 +37,12 @@ const RelativeToRange = {
 // margin
 const DEFAULT_THRESHOLD_MARGIN = 5;
 
+// Min 10 databases per 100 processing units.
+// https://cloud.google.com/spanner/quotas#database-limits
+const DATABASES_PER_100_PU = 10;
+
 const {logger} = require('../../../autoscaler-common/logger');
+const {AutoscalerUnits} = require('../../../autoscaler-common/types');
 
 /**
  * @typedef {import('../../../autoscaler-common/types').AutoscalerSpanner
@@ -170,6 +175,21 @@ function loopThroughSpannerMetrics(spanner, getSuggestedSize) {
   });
 
   let maxSuggestedSize = spanner.minSize;
+
+  if (
+    spanner.units === AutoscalerUnits.PROCESSING_UNITS &&
+    spanner.numDatabases
+  ) {
+    const minUnitsForNumDatabases =
+      Math.ceil(spanner.numDatabases / DATABASES_PER_100_PU) * 100;
+    logger.info({
+      message: `\tMinumum ${minUnitsForNumDatabases} ${spanner.units} required for ${spanner.numDatabases} databases`,
+      projectId: spanner.projectId,
+      instanceId: spanner.instanceId,
+    });
+    maxSuggestedSize = Math.max(maxSuggestedSize, minUnitsForNumDatabases);
+  }
+
   spanner.isOverloaded = false;
 
   for (const metric of /** @type {SpannerMetricValue[]} */ (spanner.metrics)) {

src/scaler/scaler-core/test/scaling-methods/base.test.js

@@ -265,4 +265,22 @@ describe('#loopThroughSpannerMetrics', () => {
     spanner.metrics[0].should.have.property('margin');
     spanner.metrics[1].should.have.property('margin').and.equal(99);
   });
+
+  it('should clamp to a min number of PU based on numDatabases', () => {
+    const spanner = /** @type {AutoscalerSpanner} */ ({
+      units: 'PROCESSING_UNITS',
+      minSize: 100,
+      numDatabases: 55,
+      currentSize: 1000,
+      maxSize: 2000,
+      metrics: [
+        {name: 'high_priority_cpu', threshold: 65, value: 10},
+        {name: 'rolling_24_hr', threshold: 90, value: 10},
+      ],
+    });
+
+    // Metrics suggest 100PU, but 55 db's requires 600 PU
+    const suggestedSize = loopThroughSpannerMetrics(spanner, () => 100);
+    suggestedSize.should.be.equal(600);
+  });
 });

src/scaler/scaler-core/test/state.test.js

@@ -104,6 +104,7 @@ const BASE_CONFIG = {
   maxSize: 200,
   stepSize: 10,
   overloadStepSize: 10,
+  numDatabases: 1,
 };
 
 describe('stateFirestoreTests', () => {