Archive Name And Parameters Vs Statistics
Initialization Parameters. Assigns the fetch archive log (FAL) client name used by the FAL server to refer to the FAL client.
Life Is Messy Demo queries have this nasty habit of being clean. Even using a pit of despair like Adventure Works or World Wide Importers, it’s easy to craft demo queries that fit the scenario you need to make yourself look like a genius.
Stack Overflow, in all its simplicity, makes this even easier (lucky me! Ibm Employee Serial Number Lookup there. ) because there’s nothing all that woogy or wonky to dance around. While working with a client recently — yes, Brent lets me talk to paying customers — we found a rather tough situation. They were using Windowing functions over one group of columns to partition and order by, but the where clause was touching a totally different group of columns. The query plan wasn’t happy. Users weren’t happy. I was still dizzy from being on a boat.
If you’ve been reading the blog for a while, you may remember from about two years ago. Over there, we talked about a POC index, a term popularized by Itzik Ben-Gan.
But how does that work when your query has other needs? Let’s meet our query! Astronaughty Oddball Let’s pause here for a minute. Stuff like this can seem witchcrafty when it’s glossed over in a blog post. The index I created is awesome for the Windowing function, and the index that SQL registered as missing was awesome for the where clause. When I have both indexes, SQL chooses the where-clause-awesome-index because it judges the query will be cheaper to deal with when it can easily seek and filter out rows from the key of the nonclustered index, and then pass only those rows along to the Windowing function. Now, it can still do this with the Windowing-function-awesome-index, because the where clause columns are included, just not as efficiently as when they’re key columns.
The trade-off here is a Sort operation to partition and order by for the Windowing function, but SQL says that will still be far cheaper to sort a bunch of data Time bomb If you’re query tuning with a small amount of data, you’ll take a look at these query costs, stick with the where clause awesome index, and go get extra drunk for doing a wicked good job. Here they are. Little Blue Spills So what’s the point?
Missing index requests don’t always have your long term health in mind when they pop up. Some may; others may just be a shot and a beer to get your query past a hangover. If I go back and run the ‘2013’ query with only the original index on there (the one that helps the Windowing function), there’s still a missing index request, but with a lower value (75% rather than 98%). Part of this is due to how costs are estimated and where SQL expects the sort to happen (disk vs memory). In our case, the Sort was a bit of a time bomb. At first, it didn’t matter. As we included more data, it got worse.
This is the kind of challenge that a lot of developers face as their app goes from a couple hundred clients to a couple thousand clients, and exactly the kind of thing our helps with. Thanks for reading! Brent says: this isn’t just about missing index hints in query plans, either: it’s also a great example of why you have to be a little bit careful with the missing index DMV recommendations, too. Would report this index as missing, and you won’t know which queries are asking for it (or whether they’ve gotten better or worse.) Every now and then, you’ll add a missing index and performance will actually get worse – so you’ve also gotta be looking at your top resource-intensive queries via. In this example, after you’ve added Clippy’s index, the now-slower query would show up in sp_BlitzCache with no missing index hints, and you’d need to know how to hand-craft your own.
Changing Parameter Values in a Parameter File You change the value of a parameter in a parameter file in one of the following ways: • By editing an initialization parameter file In most cases, the new value takes effect the next time you start an instance of the database. • By issuing an ALTER SYSTEM SET. SCOPE=SPFILE statement to update a server parameter file • By issuing an ALTER SYSTEM RESET. SCOPE=SPFILE statement to remove a parameter from a server parameter file, causing the default value to take effect the next time you start an instance of the database.
Modifiable Parameters Some initialization parameters can be modified using the ALTER SESSION or ALTER SYSTEM statements while an instance is running. Use the following syntax to modify initialization parameters: ALTER SESSION SET parameter_name = value ALTER SYSTEM SET parameter_name = value [DEFERRED] Whenever a parameter is modified using the ALTER SYSTEM statement, the Oracle Database records the statement that modifies the parameter in the alert log. The ALTER SESSION statement changes the value of the specified parameter for the duration of the session that invokes the statement. The value of the parameter does not change for other sessions in the instance. When Parameters Are Set Incorrectly Some parameters have a minimum setting below which an Oracle instance will not start.
For other parameters, setting the value too low or too high may cause Oracle to perform badly, but it will still run. Also, Oracle may convert some values outside the acceptable range to usable levels. If a parameter value is too low or too high, or you have reached the maximum for some resource, then Oracle returns an error.
Frequently, you can wait a short while and retry the operation when the system is not as busy. If a message occurs repeatedly, then you should shut down the instance, adjust the relevant parameter, and restart the instance. Scripting on this page enhances content navigation, but does not change the content in any way.