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AW-argh

This is another of the blog notes that have been sitting around for several years – in this case since May 2014, based on a script I wrote a year earlier. It makes an important point about “inconsistency” of timing in the way that Oracle records statistics of work done. As a consequence of being first drafted in May 2014 the original examples showed AWR results from 10.2.0.5 and 11.2.0.4 – I’ve just run the same test on 19.3.0.0 to see if anything has changed.

 

Troubleshooting

A recent thread on the Oracle Developer Community starts with the statement that a query is taking a very long time (with the question “how do I make it go faster?” implied rather than asked). It’s 12.1.0.2 (not that that’s particularly relevant to this blog note), and we have been given a number that quantifies “very long time” (again not particularly relevant to this blog note – but worth mentioning because your “slow” might be my “wow! that was fast” and far too many people use qualitative adjectives when the important detail is quantative). The query had already been running for 15 hours – and here it is:

Optimizer Tricks 1

I’ve got a number of examples of clever little tricks the optimizer can do to transform your SQL before starting in on the arithmetic of optimisation. I was prompted to publish this one by a recent thread on ODC. It’s worth taking note of these tricks when you spot one as a background knowledge of what’s possible makes it much easier to interpret and trouble-shoot from execution plans. I’ve labelled this one “#1” since I may publish a few more examples in the future, and then I’ll have to catalogue them – but I’m not making any promises about that.

Here’s a table definition, and a query that’s hinted to use an index on that table.

sql_patch

This note is a short follow-up to a note I wrote some time ago about validating foreign key constraints where I examined the type of SQL Oracle generates internally to do the validation between parent and child tables.  In that article I suggested (before testing) that you could create an SQL patch for the generated SQL to over-ride the plan taken by Oracle – a plan dictated to some extent by hints (including a “deprecated” ordered hint) embedded in the code. I did say that the strategy might not work for SQL optimised by SYS, but it turned out that it did.

Here’s a little script I ran to test a few variations on the theme:

Join View

It’s strange how one thing leads to another when you’re trying to check some silly little detail. This morning I wanted to find a note I’d written about the merge command and “stable sets”, and got to a draft about updatable join views that I’d started in 2016 in response to a question on OTN (as it was at the time) and finally led to a model that I’d written in 2008 showing that the manuals were wrong.

ORA-14300 partitioning key maps to a partition outside maximum permitted number of partitions and NULLs

While researching interval partitioning in Oracle 19c I came across a phenomenon I had already solved a long time ago but then forgot about. This time I decided to write about it so I don’t have to spend 5 minutes rediscovering the wheel. As always, if you are following along, make sure you are appropriately licensed for this feature

The Situation

Consider the following example:

Oracle Connection Manager (CMAN) quick reporting script

Oracle Connection Manager (CMAN) quick reporting scripts

Here are a few scripts I use to parse Connection Manager “show service”

List services registered by instance

CMCTL can show the services in a long list, but I want something quick like this, with one line per service, and one column per endpoint that registers to CMAN:

script output, a bit obfuscated

The following script

gather_system_stats

What happens when you execute dbms_stats.gather_system_stats() with the ‘Exadata’ option ?

Here’s what my system stats look like (12.2.0.1 test results) after doing so. (The code to generate the two different versions is at the end of the note).

Azure VMs with Oracle- Next Steps

Microsoft has done a great job of documenting how to create a VM with the appropriate VM image and Oracle version, then how to log in, startup the listener and create the database.  I just have some enhancements I’d like to make to it, hoping to help it move up one level.

I Bequeath to You

All instructions provided by the Microsoft documentation show how to connect to the database using a bequeath, (BEQ) connection.  This is done by the following command, using SQL Plus, (or similar):

sqlplus / as sysdba

It bypasses the need for a connection string, only requiring the SID to be set at the environment level:

export ORACLE_SID=

This information, for Oracle DBAs, is often gathered from a running database server executing the following command:

How 19c Auto Indexes are named?

As a SQL_ID-like base 32 hash on table owner, name, column list

The indexes created by the 19c Auto Indexing feature have a generated name like: “SYS_AI_gg1ctjpjv92d5”. I don’t like to rely on the names: there’s an AUTO column in DBA_INDEXES to flag the indexes created automatically.

But, one thing is very nice: the name is not random. The same index (i.e on same table and columns) will always have the same name. Even when dropped and re-created. Even when created in a different database. This is very nice to follow them (like quickly searching in my e-mails and find the same issue encountered in another place). Like we do with SQL_ID.

Yes, the generation of the name is similar to SQL_ID as it is the result of a 64-bit number from a hash function, displayed in base 32 with alphanumeric characters.