move data to db or cache based on the change of state of enableRedisS…

…ampleStore flag

cache/sampleStore.js

@@ -40,6 +40,7 @@ const constants = {
   persistInProgressKey: PFX + SEP + 'persistInProgress',
   prefix: PFX,
   separator: SEP,
+  previousStatusKey: PFX + SEP + 'previousSampleStoreStatus',
 };
 
 /**

cache/sampleStoreInit.js

@@ -18,8 +18,27 @@ const Subject = require('../db').Subject;
 const featureToggles = require('feature-toggles');
 const redisClient = require('./redisCache').client.sampleStore;
 const samsto = require('./sampleStore');
+const samstoPersist = require('./sampleStorePersist');
 const constants = samsto.constants;
 
+/**
+ * Deletes the key that does the previous value of the "enableRedisSampleStore"
+ * flag.
+ * @returns {Promise} - which resolves to 0 when the key is deleted.
+ */
+function deletePreviousStatus() {
+  return redisClient.delAsync(constants.previousStatusKey);
+} // deletePreviousStatus
+
+/**
+ * Gets the value of "previousStatusKey"
+ *
+ * @returns {Promise} which resolves to the value of the previoiusStatusKey
+ */
+function getPreviousStatus() {
+  return redisClient.getAsync(constants.previousStatusKey);
+} // persistInProgress
+
 /**
  * Clear all the "sampleStore" keys (for subjects, aspects, samples) from
  * redis.
@@ -38,7 +57,8 @@ function eradicate() {
       console.error(err); // eslint-disable-line no-console
       Promise.resolve(true);
     }));
-  return Promise.all(promises);
+  return deletePreviousStatus()
+    .then(() => Promise.all(promises));
 } // eradicate
 
 /**
@@ -153,10 +173,6 @@ function populateSamples() {
  *  false if the feature is not enabled.
  */
 function populate() {
-  if (!featureToggles.isFeatureEnabled(constants.featureName)) {
-    return Promise.resolve(false);
-  }
-
   const msg = 'Populating redis sample store from db';
   console.log(msg); // eslint-disable-line no-console
 
@@ -165,51 +181,73 @@ function populate() {
 } // populate
 
 /**
- * Checks whether the sample store exists by counting the members of the three
- * index keys (samples, subjects, aspects). If any has more than one member,
- * consider the sample store as existing.
  *
- * Note: I tried using the redis "exists" command but our travis build kept
- * failing with a message that I was passing the wrong number of args to the
- * "exists" command. I gave up and went with counting members using "scard"
- * instead.
+ * Compare the current status of the "enableRedisSampleStore" flag with its
+ * previous status. If both current status and previous status are the same, do
+ * nothing. When the current status and the previous status do not match, take
+ * some action depending on the current status.
  *
  * @returns {Promise} which resolves to true if the sample store already
  *  exists.
  */
-function sampleStoreExists() {
-  const cmds = [
-    ['scard', constants.indexKey.aspect],
-    ['scard', constants.indexKey.sample],
-    ['scard', constants.indexKey.subject],
-  ];
-  return redisClient.batch(cmds).execAsync()
-  .then((batchResponse) =>
-    batchResponse[0] > 0 || // eslint-disable-line no-magic-numbers
-    batchResponse[1] > 0 || // eslint-disable-line no-magic-numbers
-    batchResponse[2] > 0); // eslint-disable-line no-magic-numbers
-} // sampleStoreExists
+function storeSampleToCacheOrDb() {
+  const currentStatus = featureToggles.isFeatureEnabled(constants.featureName)
+                                          || false;
+  return getPreviousStatus()
+  .then((prevState) => {
+    const previousStatus = (prevState == 'true') || false;
+
+    // set the previousStatus to the currentStatus
+    redisClient.setAsync(constants.previousStatusKey, currentStatus);
+
+    /*
+     * when the current status and the previous status do not match, actions
+     * needs to be taken based on the current status
+    */
+    if (previousStatus !== currentStatus) {
+      /*
+       * call "popluate" when "enableRedisSampleStore" flag has been changed
+       * from false to true. Call "eradicate" and "storeSampleToDb" when
+       * "enableRedisSampleStore" flag has been changed from true to false
+       */
+      if (currentStatus) {
+        return populate();
+      }
+
+      /*
+       * If samples are being persisted to the db by some other process, STOP
+       * and resolve to false.
+       */
+      return samstoPersist.persistInProgress()
+      .then((inProgress) => {
+        if (inProgress) {
+          return Promise.resolve(false);
+        }
+
+        return samstoPersist.storeSampleToDb();
+      }).then(() => eradicate()); // eradicate the cache
+    }
+
+    // when the current status and previous status are same, resolve to false
+    return Promise.resolve(false);
+  });
+} // storeSampleToCacheOrDb
 
 /**
- * Initializes the redis sample store from the db if the feature is enabled and
- * the sample store index keys do not already exist.
+ * Calls "storeSampleToCacheOrDb" to either populate the cache from db or db
+ * from cache, depending on the change of state of the "enableRedisSampleStore"
+ * flag
  *
- * @returns {Promise} which resolves to true if sample store is enabled and
- *  has completed initialization; resolves to false if feature is not
- *  enabled.
+ * @returns {Promise} which resolves to false if no action was taken or resolves
+ * to a list of promises if some action was taken.
  */
 function init() {
-  if (!featureToggles.isFeatureEnabled(constants.featureName)) {
-    return Promise.resolve(false);
-  }
-
-  return sampleStoreExists()
-  .then((exists) => {
-    if (exists) {
-      return Promise.resolve(true);
-    }
-
-    return populate();
+  return storeSampleToCacheOrDb()
+  .then((ret) => Promise.resolve(ret))
+  .catch((err) => {
+    // NO-OP
+    console.error(err); // eslint-disable-line no-console
+    Promise.resolve(false);
   });
 } // init
 

cache/sampleStorePersist.js

@@ -30,9 +30,33 @@ function persistInProgress() {
 } // persistInProgress
 
 /**
- * Truncate the sample table in the db and persist all the samples from redis
+ * Truncate the sample table in the DB and persist all the samples from redis
  * into the empty table.
  *
+ * @returns {Promise} - which resolves to true once the sample is persisted to
+ * the database
+ */
+function storeSampleToDb() {
+  return redisClient.setAsync(constants.persistInProgressKey, 'true')
+  .then(() => Sample.destroy({ truncate: true, force: true }))
+  .then(() => redisClient.smembersAsync(constants.indexKey.sample))
+  .then((keys) => keys.map((key) => ['hgetall', key]))
+  .then((cmds) => redisClient.batch(cmds).execAsync())
+  .then((res) => {
+    const samplesToCreate = res.map((sample) => {
+      sample.relatedLinks = JSON.parse(sample.relatedLinks);
+      return sample;
+    });
+    return Sample.bulkCreate(samplesToCreate);
+  })
+  .then(() => redisClient.delAsync(constants.persistInProgressKey))
+  .then(() => console.log('persisted redis sample store to db'))
+  .then(() => true);
+} // storeSampleToDb
+
+/**
+ * Calls the storeSampleToDb function to store sample data back to DB.
+ *
  * @returns {Promise} which resolves to true upon complete if redis sample
  * store feature is enabled, or false on error or if feature is disabled or if
  * there is already a persist in progress.
@@ -45,25 +69,11 @@ function persist() {
   return persistInProgress()
   .then((alreadyInProgress) => {
     if (alreadyInProgress) {
-      Promise.resolve(false);
+      return Promise.resolve(false);
     }
 
-    return redisClient.setAsync(constants.persistInProgressKey, 'true');
+    return storeSampleToDb();
   })
-  .then(() => Sample.destroy({ truncate: true, force: true }))
-  .then(() => redisClient.smembersAsync(constants.indexKey.sample))
-  .then((keys) => keys.map((key) => ['hgetall', key]))
-  .then((cmds) => redisClient.batch(cmds).execAsync())
-  .then((res) => {
-    const samplesToCreate = res.map((sample) => {
-      sample.relatedLinks = JSON.parse(sample.relatedLinks);
-      return sample;
-    });
-    return Sample.bulkCreate(samplesToCreate);
-  })
-  .then(() => redisClient.delAsync(constants.persistInProgressKey))
-  .then(() => console.log('persisted redis sample store to db'))
-  .then(() => true)
   .catch((err) => {
     // NO-OP
     console.error(err); // eslint-disable-line no-console
@@ -74,4 +84,5 @@ function persist() {
 module.exports = {
   persist,
   persistInProgress,
+  storeSampleToDb,
 };

index.js

@@ -127,7 +127,11 @@ function start() { // eslint-disable-line max-statements
     });
   }
 
-  // Make sure sample store is initialized if feature is enabled.
+  /*
+   * Based on the change of state of the "enableSampleStore" feature flag
+   * populate the data into the cache or dump the data from the cache into the
+   * db
+   */
   sampleStore.init();
 
   /*

tests/cache/sampleStore.js

@@ -174,7 +174,7 @@ describe('sampleStore (feature on):', () => {
         .to.be.true;
     })
     .then(() => samstoinit.init())
-    .then((res) => expect(res).to.be.true)
+    .then((res) => expect(res).to.not.be.false)
     .then(() => done())
     .catch(done);
   });