What keeps putForExternalRead from suffering the thundering-

[memoryerror]

We have code that looks like this:

Data getSomeData(key)
{
Data theData = theCache.get(node, key);

if (theData == null)
{
theData = read the data from database
theCache.putForExternalRead(node, key, the data from database);

return theData;
}

Now suppose we have a bunch of threads that hit getSomeData at the same time with the same key.

Will several threads get a null data, read from the database, and do the putForExternalRead, with only the first call to putForExternalRead having any effect?

It would be desirable not to have to pay the overhead of multiple database reads in this situation.

[dukehoops]

fwiw, I have exactly the same question

[memoryerror]

I asked jboss support, and they said: "Yes, if multiple threads hit the same data at the same time they would each get a null and read from the database. To prevent this, you\'d need to use SERIALIZABLE isolation. But it does not scale, so unless you do have nodes hitting the same data at the same time extremely frequently, you would see worse overall performance."