Hello,
I use H2 as an embedded, in-memory database, exclusively for temp
tables. I would like to contribute the following small patch, which has
improved the throughput of certain use cases in our system by 18-30%.
diff --git a/h2/src/main/org/h2/engine/Session.java
b/h2/src/main/org/h2/engine/Session.java
index 215d814..4161c72 100644
--- a/h2/src/main/org/h2/engine/Session.java
+++ b/h2/src/main/org/h2/engine/Session.java
@@ -928,11 +928,13 @@ public class Session extends SessionWithState {
private void cleanTempTables(boolean closeSession) {
if (localTempTables != null && localTempTables.size() > 0) {
synchronized (database) {
- for (Table table :
New.arrayList(localTempTables.values())) {
+ Iterator<Table> itr = localTempTables.values().iterator();
+ while (itr.hasNext()) {
+ Table table = itr.next();
if (closeSession || table.getOnCommitDrop()) {
modificationId++;
table.setModified();
- localTempTables.remove(table.getName());
+ itr.remove();
table.removeChildrenAndResources(this);
if (closeSession) {
// need to commit, otherwise recovery might
Specifically, the call to New.arrayList(localTempTables.values()) at the
top of the for loop was the bottleneck that stood out while profiling
our system. I imagine it originally was written this way to avoid a
ConcurrentModificationException, but using the Iterator.remove() call
does the same thing much more efficiently.
This is based on the code in GitHub as of last night. It is just copied
from git's diff output. If you need me to submit this in another form,
please let me know.
Thanks for producing and sharing a great project!
Best regards,
Eric
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