misc review improvements

community/community-it/cypher-it/src/test/scala/org/neo4j/internal/collector/DataCollectorMatchers.scala

@@ -199,7 +199,7 @@ object DataCollectorMatchers {
               errors += s"Expected value '$expectedValue' at position $i, but list was too small"
           }
           if (values.size > expected.size)
-            errors += s"Expected list of maxSize ${expected.size}, but got additional elements ${values.slice(expected.size, values.size)}"
+            errors += s"Expected list of ${expected.size} elements, but got additional elements ${values.slice(expected.size, values.size)}"
 
         case x =>
           errors += s"Expected list but got '$x'"

community/community-it/cypher-it/src/test/scala/org/neo4j/internal/collector/DataCollectorQueriesAcceptanceTest.scala

@@ -298,13 +298,10 @@ class DataCollectorQueriesAcceptanceTest extends DataCollectorTestSupport {
 
   test("[retrieveAllAnonymized] should anonymize tokens inside queries") {
     // given
-    execute("CALL db.stats.stop('QUERIES')").single
     execute("CREATE (:User {age: 99})-[:KNOWS]->(:Buddy {p: 42})-[:WANTS]->(:Raccoon)") // create tokens
 
-    execute("CALL db.stats.collect('QUERIES')").single
     execute("MATCH (:User)-[:KNOWS]->(:Buddy)-[:WANTS]->(:Raccoon) RETURN 1")
     execute("MATCH ({p: 42}), ({age: 43}) RETURN 1")
-    execute("CALL db.stats.stop('QUERIES')").single
 
     // when
     val res = execute("CALL db.stats.retrieveAllAnonymized('myToken')")
@@ -319,10 +316,9 @@ class DataCollectorQueriesAcceptanceTest extends DataCollectorTestSupport {
   test("[retrieveAllAnonymized] should handle pre-parser options") {
     // given
     execute("CREATE (:User {age: 99})-[:KNOWS]->(:Buddy {p: 42})-[:WANTS]->(:Raccoon)") // create tokens
-    execute("CALL db.stats.collect('QUERIES')").single
+
     execute("EXPLAIN MATCH (:User)-[:KNOWS]->(:Buddy)-[:WANTS]->(:Raccoon) RETURN 1")
     execute("CYPHER 3.4 runtime=interpreted PROFILE CREATE ()")
-    execute("CALL db.stats.stop('QUERIES')").single
 
     // when
     val res = execute("CALL db.stats.retrieveAllAnonymized('myToken')")
@@ -338,10 +334,9 @@ class DataCollectorQueriesAcceptanceTest extends DataCollectorTestSupport {
     // given
     val path = Files.createTempFile("data", ".csv")
     val url = path.toUri.toURL.toString
-    execute("CALL db.stats.collect('QUERIES')").single
+
     execute(s"LOAD CSV FROM '$url' AS row CREATE ({key: row[0]})")
     execute(s"USING PERIODIC COMMIT 30 LOAD CSV FROM '$url' AS row CREATE ({key: row[0]})")
-    execute("CALL db.stats.stop('QUERIES')").single
 
     // when
     val res = execute("CALL db.stats.retrieveAllAnonymized('myToken')")

community/data-collector/src/main/java/org/neo4j/internal/collector/DataCollectorProcedures.java

@@ -19,9 +19,7 @@
  */
 package org.neo4j.internal.collector;
 
-import java.time.ZonedDateTime;
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.Map;
 import java.util.stream.Stream;
 
@@ -63,7 +61,7 @@ public Stream<RetrieveResult> retrieve( @Name( value = "section" ) String sectio
             return TokensSection.retrieve( dataCollector.kernel );
 
         case Sections.META:
-            return MetaSection.retrieve( null, dataCollector.kernel, dataCollector.queryCollector.nSilentQueryDrops() );
+            return MetaSection.retrieve( null, dataCollector.kernel, dataCollector.queryCollector.numSilentQueryDrops() );
 
         case Sections.QUERIES:
             return QueriesSection.retrieve( dataCollector.queryCollector.getData(),
@@ -87,7 +85,7 @@ public Stream<RetrieveResult> retrieveAllAnonymized( @Name( value = "graphToken"
             throw new InvalidArgumentsException( "Graph token must be a non-empty string" );
         }
 
-        return Stream.of( MetaSection.retrieve( graphToken, dataCollector.kernel, dataCollector.queryCollector.nSilentQueryDrops() ),
+        return Stream.of( MetaSection.retrieve( graphToken, dataCollector.kernel, dataCollector.queryCollector.numSilentQueryDrops() ),
                           GraphCountsSection.retrieve( dataCollector.kernel, Anonymizer.IDS ),
                           QueriesSection.retrieve( dataCollector.queryCollector.getData(),
                                                    new IdAnonymizer( transaction.tokenRead() ),

community/data-collector/src/main/java/org/neo4j/internal/collector/MetaSection.java

@@ -45,7 +45,9 @@ private MetaSection()
     { // only static methods
     }
 
-    static Stream<RetrieveResult> retrieve( String graphToken, Kernel kernel, long nSilentQueryDrops ) throws TransactionFailureException
+    static Stream<RetrieveResult> retrieve( String graphToken,
+                                            Kernel kernel,
+                                            long numSilentQueryDrops ) throws TransactionFailureException
     {
         Map<String, Object> systemData = new HashMap<>();
         systemData.put( "jvmMemoryFree", Runtime.getRuntime().freeMemory() );
@@ -77,7 +79,7 @@ static Stream<RetrieveResult> retrieve( String graphToken, Kernel kernel, long n
         systemData.put( "fileEncoding",  System.getProperty( "file.encoding" ) );
 
         Map<String, Object> internalData = new HashMap<>();
-        internalData.put( "numSilentQueryCollectionMisses", nSilentQueryDrops );
+        internalData.put( "numSilentQueryCollectionMisses", numSilentQueryDrops );
 
         Map<String, Object> metaData = new HashMap<>();
         metaData.put( "graphToken", graphToken );

community/data-collector/src/main/java/org/neo4j/internal/collector/QueryCollector.java

@@ -48,18 +48,27 @@ class QueryCollector extends CollectorStateMachine<Iterator<QuerySnapshot>> impl
     private volatile boolean isCollecting;
     private final RingRecentBuffer<QuerySnapshot> queries;
     private final JobScheduler jobScheduler;
+    /**
+     * We retain at max 2^13 = 8192 queries in memory at any given time. This number
+     * was chosen as a trade-off between getting a useful amount of queries, and not
+     * wasting too much heap. Even with a buffer full of unique queries, the estimated
+     * footprint lies in tens of MBs. If the buffer is full of cached queries, the
+     * retained size was measured to 265 kB.
+     */
+    private static final int QUERY_BUFFER_SIZE_IN_BITS = 13;
 
     QueryCollector( JobScheduler jobScheduler )
     {
         super( true );
         this.jobScheduler = jobScheduler;
         isCollecting = false;
-        queries = new RingRecentBuffer<>( 13 );
+
+        queries = new RingRecentBuffer<>( QUERY_BUFFER_SIZE_IN_BITS );
     }
 
-    long nSilentQueryDrops()
+    long numSilentQueryDrops()
     {
-        return queries.nSilentQueryDrops();
+        return queries.numSilentQueryDrops();
     }
 
     // CollectorStateMachine

community/data-collector/src/main/java/org/neo4j/internal/collector/RingRecentBuffer.java

@@ -53,7 +53,7 @@ public RingRecentBuffer( int bitSize )
         dropEvents = new AtomicLong( 0 );
     }
 
-    long nSilentQueryDrops()
+    long numSilentQueryDrops()
     {
         return dropEvents.get();
     }

community/data-collector/src/test/scala/org/neo4j/internal/collector/RingRecentBufferTest.java

@@ -62,7 +62,7 @@ void shouldJustWork()
         }
         buffer.foreach( Assertions::assertNotNull );
 
-        assertEquals( 0, buffer.nSilentQueryDrops() );
+        assertEquals( 0, buffer.numSilentQueryDrops() );
     }
 
     @Test
@@ -100,7 +100,7 @@ void shouldNotReadSameElementTwice() throws ExecutionException, InterruptedExcep
         {
             executor.shutdown();
         }
-        assertEquals( 0, buffer.nSilentQueryDrops() );
+        assertEquals( 0, buffer.numSilentQueryDrops() );
     }
 
     @Test
@@ -133,7 +133,7 @@ void shouldNeverReadUnwrittenElements() throws ExecutionException, InterruptedEx
         {
             executor.shutdown();
         }
-        assertEquals( 0, buffer.nSilentQueryDrops() );
+        assertEquals( 0, buffer.numSilentQueryDrops() );
     }
 
     @Test
@@ -170,7 +170,7 @@ void shouldWorkWithManyConcurrentProducers() throws ExecutionException, Interrup
         {
             executor.shutdown();
         }
-        assertEquals( 0, buffer.nSilentQueryDrops() );
+        assertEquals( 0, buffer.numSilentQueryDrops() );
     }
 
     private <T> Runnable stress( int n, LongConsumer action )