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perf: prepare sessions with r/w tx in-process
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Preparing sessions with a read/write transaction using a background
executor works well as long as that executor is not being overloaded.
When the executor has reached its limit, it is more efficient to allow
the read/write transaction to be created in-process, as that scales
with the number of user threads available, instead of being limited to
the fixed thread pool of the background executor.

Fixes #151
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@olavloite
olavloite committed Apr 14, 2020
1 parent 4669c02 commit 8cb79a5
Showing 1 changed file with 110 additions and 41 deletions.
151 changes: 110 additions & 41 deletions google-cloud-spanner/src/main/java/com/google/cloud/spanner/SessionPool.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1093,6 +1093,7 @@ private static enum Position {
private final ScheduledExecutorService executor;
private final ExecutorFactory<ScheduledExecutorService> executorFactory;
private final ScheduledExecutorService prepareExecutor;
private final int prepareThreadPoolSize;
final PoolMaintainer poolMaintainer;
private final Clock clock;
private final Object lock = new Object();
Expand Down Expand Up @@ -1137,6 +1138,12 @@ private static enum Position {
@GuardedBy("lock")
private long numSessionsReleased = 0;

@GuardedBy("lock")
private long numSessionsInProcessPrepared = 0;

@GuardedBy("lock")
private long numSessionsAsyncPrepared = 0;

private AtomicLong numWaiterTimeouts = new AtomicLong();

@GuardedBy("lock")
Expand Down Expand Up @@ -1213,15 +1220,14 @@ private SessionPool(
this.options = options;
this.executorFactory = executorFactory;
this.executor = executor;
int prepareThreads;
if (executor instanceof ThreadPoolExecutor) {
prepareThreads = Math.max(((ThreadPoolExecutor) executor).getCorePoolSize(), 1);
prepareThreadPoolSize = Math.max(((ThreadPoolExecutor) executor).getCorePoolSize(), 1);
} else {
prepareThreads = 8;
prepareThreadPoolSize = 8;
}
this.prepareExecutor =
Executors.newScheduledThreadPool(
prepareThreads,
prepareThreadPoolSize,
new ThreadFactoryBuilder()
.setDaemon(true)
.setNameFormat("session-pool-prepare-%d")
Expand All @@ -1232,6 +1238,20 @@ private SessionPool(
this.initMetricsCollection(metricRegistry, labelValues);
}

@VisibleForTesting
long getNumberOfSessionsInProcessPrepared() {
synchronized (lock) {
return numSessionsInProcessPrepared;
}
}

@VisibleForTesting
long getNumberOfSessionsAsyncPrepared() {
synchronized (lock) {
return numSessionsAsyncPrepared;
}
}

@VisibleForTesting
int getNumberOfAvailableWritePreparedSessions() {
synchronized (lock) {
Expand Down Expand Up @@ -1416,46 +1436,93 @@ PooledSession getReadSession() throws SpannerException {
PooledSession getReadWriteSession() {
Span span = Tracing.getTracer().getCurrentSpan();
span.addAnnotation("Acquiring read write session");
Waiter waiter = null;
PooledSession sess = null;
synchronized (lock) {
if (closureFuture != null) {
span.addAnnotation("Pool has been closed");
throw new IllegalStateException("Pool has been closed");
// Loop to retry SessionNotFoundExceptions that might occur during in-process prepare of a
// session.
while (true) {
Waiter waiter = null;
boolean inProcessPrepare = false;
synchronized (lock) {
if (closureFuture != null) {
span.addAnnotation("Pool has been closed");
throw new IllegalStateException("Pool has been closed");
}
if (resourceNotFoundException != null) {
span.addAnnotation("Database has been deleted");
throw SpannerExceptionFactory.newSpannerException(
ErrorCode.NOT_FOUND,
String.format(
"The session pool has been invalidated because a previous RPC returned 'Database not found': %s",
resourceNotFoundException.getMessage()),
resourceNotFoundException);
}
sess = writePreparedSessions.poll();
if (sess == null) {
if (numSessionsBeingPrepared <= prepareThreadPoolSize) {
if (numSessionsBeingPrepared <= readWriteWaiters.size()) {
PooledSession readSession = readSessions.poll();
if (readSession != null) {
span.addAnnotation(
"Acquired read only session. Preparing for read write transaction");
prepareSession(readSession);
} else {
span.addAnnotation("No session available");
maybeCreateSession();
}
}
} else {
inProcessPrepare = true;
numSessionsInProcessPrepared++;
PooledSession readSession = readSessions.poll();
if (readSession != null) {
// Create a read/write transaction in-process if there is already a queue for prepared
// sessions. This is more efficient than doing it asynchronously, as it scales with
// the number of user threads. The thread pool for asynchronously preparing sessions
// is fixed.
span.addAnnotation(
"Acquired read only session. Preparing in-process for read write transaction");
sess = readSession;
} else {
span.addAnnotation("No session available");
maybeCreateSession();
}
}
if (sess == null) {
waiter = new Waiter();
if (inProcessPrepare) {
readWaiters.add(waiter);
} else {
readWriteWaiters.add(waiter);
}
}
} else {
span.addAnnotation("Acquired read write session");
}
}
if (resourceNotFoundException != null) {
span.addAnnotation("Database has been deleted");
throw SpannerExceptionFactory.newSpannerException(
ErrorCode.NOT_FOUND,
String.format(
"The session pool has been invalidated because a previous RPC returned 'Database not found': %s",
resourceNotFoundException.getMessage()),
resourceNotFoundException);
if (waiter != null) {
logger.log(
Level.FINE,
"No session available in the pool. Blocking for one to become available/created");
span.addAnnotation("Waiting for read write session to be available");
sess = waiter.take();
}
sess = writePreparedSessions.poll();
if (sess == null) {
if (numSessionsBeingPrepared <= readWriteWaiters.size()) {
PooledSession readSession = readSessions.poll();
if (readSession != null) {
span.addAnnotation("Acquired read only session. Preparing for read write transaction");
prepareSession(readSession);
} else {
span.addAnnotation("No session available");
maybeCreateSession();
if (inProcessPrepare) {
try {
sess.prepareReadWriteTransaction();
} catch (Throwable t) {
sess = null;
SpannerException e = newSpannerException(t);
if (!isClosed()) {
handlePrepareSessionFailure(e, sess, false);
}
if (!isSessionNotFound(e)) {
throw e;
}
}
waiter = new Waiter();
readWriteWaiters.add(waiter);
} else {
span.addAnnotation("Acquired read write session");
}
}
if (waiter != null) {
logger.log(
Level.FINE,
"No session available in the pool. Blocking for one to become available/created");
span.addAnnotation("Waiting for read write session to be available");
sess = waiter.take();
if (sess != null) {
break;
}
}
sess.markBusy();
incrementNumSessionsInUse();
Expand Down Expand Up @@ -1583,7 +1650,8 @@ private void handleCreateSessionsFailure(SpannerException e, int count) {
}
}

private void handlePrepareSessionFailure(SpannerException e, PooledSession session) {
private void handlePrepareSessionFailure(
SpannerException e, PooledSession session, boolean informFirstWaiter) {
synchronized (lock) {
if (isSessionNotFound(e)) {
invalidateSession(session);
Expand All @@ -1606,7 +1674,7 @@ private void handlePrepareSessionFailure(SpannerException e, PooledSession sessi
MoreObjects.firstNonNull(
this.resourceNotFoundException,
isDatabaseOrInstanceNotFound(e) ? (ResourceNotFoundException) e : null);
} else if (readWriteWaiters.size() > 0) {
} else if (informFirstWaiter && readWriteWaiters.size() > 0) {
releaseSession(session, Position.FIRST);
readWriteWaiters.poll().put(e);
} else {
Expand Down Expand Up @@ -1755,6 +1823,7 @@ public void run() {
sess.prepareReadWriteTransaction();
logger.log(Level.FINE, "Session prepared");
synchronized (lock) {
numSessionsAsyncPrepared++;
numSessionsBeingPrepared--;
if (!isClosed()) {
if (readWriteWaiters.size() > 0) {
Expand All @@ -1770,7 +1839,7 @@ public void run() {
synchronized (lock) {
numSessionsBeingPrepared--;
if (!isClosed()) {
handlePrepareSessionFailure(newSpannerException(t), sess);
handlePrepareSessionFailure(newSpannerException(t), sess, true);
}
}
}
Expand Down

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