On Mar 31, 2009, at 8:16 AM, Jeff Schmitz wrote:
Thanks David,
Yes, from reading the Apple docs and wiki and prior discussions,
I'm using pre-fetching pretty extensively, and have things pretty
well tuned in that regard I think. Some of my pre-fetches are quite
large (up to 6-7 seconds under good circumstances) but they do help
bring down the overall processing time considerably. What's
interesting is that under load, the prefetches themselves start to
take longer and longer until they start taking over 10 times longer
to complete. I would have thought during the pre-fetch the DB would
be locked, so I was surprised to see this, but then I'm no DB expert
by a long shot.
I believe that this is going to depend on how the plugin for your DB
is written. I don't believe that normal reads are going to lock the
table. I know the SQL Server plugin does for the optimistic locking
check prior to updates and deletes.
Anyway, here's the prefetch code used by the background task:
ERXFetchSpecification poolFetch = new
ERXFetchSpecification(_Pool.ENTITY_NAME, poolQual, null);
NSArray <String> keyPaths = new NSArray(new String[]
{Pool.ENTRIES_KEY ,
Pool.ENTRIES_KEY + "." + Entry.COMBO_TEAMS_KEY,
Pool.ENTRIES_KEY + "." + Entry.COMBO_TEAMS_KEY + "." +
ComboTeam.TEAM_POPUPS_KEY,
Pool.ENTRIES_KEY + "." + Entry.ENTRY_SCORE_KEY,
Pool.ENTRIES_KEY + "." + Entry.ENTRY_ADMIN_KEY,
Pool.ENTRIES_KEY + "." + Entry.PLACE_INFOS_KEY});
poolFetch.setPrefetchingRelationshipKeyPaths(keyPaths);
poolFetch.setRefreshesRefetchedObjects(false);
Pool pool = (Pool)
ec.objectsWithFetchSpecification(poolFetch).lastObject();
A typical fetch might involve the following number of rows:
1 Pool---100>>Entry----63>>ComboTeams----2>>TeamPopups
Entry----1>EntryScore
Entry----1>EntryAdmin
Entry----1>PlaceInfos
Note that this is run on a brand new EO and OBS stack, so I set
refreshesRefetchedObjects to false. One other phenomenon I've
noticed is that running two instances of my app also tends to kill
performance. I do have -WOAllowsConcurrentRequestHandling YES set
in the javamonitor config.
It really sounds like the bottleneck is the DB itself and not in
Java / EOF. Which brings us to what Andrew Lindesay calls "scaling
opportunities at the database end".
Did you turn on the SQL Logging?
Dave
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