When you create a Microsoft Access 2003 link to an Oracle table using Oracle's ODBC driver, you are sometimes asked to state which columns are the primary key(s).
I would like to know how to change that initial assignment, or even how to get Access/ODBC to forget the assignment. In my limited testing I wonder if the assignment isn't cached by the ODBC driver itself.
The columns I initial chose are not correct.
Update: I never did get a full answer on this one, deleting the links then restoring them didn't work. I think it's an obscure bug. I've moved on and haven't had to worry about this oddity since.
You must delete the link to the table and create a new one. When a table is linked all the connection info about the table's path, structure (including primary key), permissions, passwords and statistics are stored in the Access db. If any of those items change in the linked table, refreshing links won't automatically update it on the Access side because Access continues to use the previously stored info. You must delete or drop the linked table and recreate the link, storing the current connection information.
Don't know for sure if this next bit also applies to odbc linked tables, but I suspect it does. For Jet tables, it's a good idea to periodically delete all links and recreate them to improve query performance, because if a linked table's statistics are made on a table with few records, once that table is filled with many more records, new statistics will tell Jet's optimizer whether using indexes or a full table scan would be the better course of action when running a query.
It is not possible to delete the link and then relink?
Related
Ok, tricky question I am trying to figure out where a database schema is storing a particular pointer. I know the pointer value I just don't what table it is in or what column. I know the pointer is 123123123. How do I check all table columns to see if any of them have that value?
Thanks.
In h2 you can use fulltext search, but then you would need to add all tables in the search scope and indexing.
If you need to index only primary keys, then it might be better but you still need to come up with individual FT_CREATE_INDEX() calls for each table. You can automate this with several languages or with ETLs (like scriptella).
If you've enough disk space, you could dump a SQL from your db and use a viewer for big files like glogg.
The advantage of the first solution is no external tools but you need to work out a specific indexing script for SQL for any existing or new table. The 2nd solution is a 1 time fix.
I use SQL Search from RedGate. It's free and it helps you find any text anywhere in the database.
https://www.red-gate.com/products/?gclid=CjwKEAjwiYG9BRCkgK-G45S323oSJABnykKAE7IH_EMhnmq7OdLdXljfIkdGZrDD6OnOrT4VB0agahoCVn3w_wcB
We have an application that generates some temporary tables and then processes the data. I dont really have control of the way the application creates this and the subsequent queries involved. What we have noticed is that Oracle uses a full table scan instead of using the index which is the primary key of the tables. If it used the primary key index the process would run a whole lot faster.
Since I do not have control over the select queries generated by the application I cannot use hints and force Oracle to use primary key index. Is there any other setting I could change somewhere that could force Oracle to use primary key index for the temporary tables?
The two most common reasons for a query not using indexes are:
It's quicker to do a full table scan.
Poor statistics.
If your queries are selecting all of the table or doing joins without mentioning a primary key in the where clause etc., chances are it's quicker to do a full scan. Without the query and indexes, and preferably an explain plan as well it's impossible to tell for certain.
I would, however, recommend that you ask your DBA to re-gather - I hope, if not gather for the first time - statistics on the table. Use dbms_stats.gather_table_stats, with an estimate percentage of 25%+.
If the tables are re-created each time the application is run then try and gather statistics after creation and primary key generation. If they are truncated and re-filled each time, then ask your DBA to rebuild them and the PK and then gather statistics as this could significantly increase query runtime.
With no control over anything I don't see how you can improve the query time any other way.
You can use hints without changing SQL by leveraging SQL Profiles. Wrap your hint(s) into a SQL Profile that takes effect for that particular SQL ID.
I understand you don't have control over SQL, I have many apps where I encounter the same restriction. After checking query structure and statistics as in Ben's post and you have proved that hinting to use the index will improve performance why not try a manually created SQL profile.
Christian Antognini has a great paper here about SQL Profiles and creating them manually. The paper mentions creating SQL Profiles manually is undocumented. I would agree undocumented, but that doesn't necessarily mean unsupported. I would say there is little documentation out there, but if you want proof that Oracle allows manual creation, check the API or look at the coe_xfr_sql_profile.sql file in the SQLT utility directory.
I also posted a cheatsheet on how to quickly manually create a SQL Profile here.
Oracle's database change notification feature sends rowids (physical row addresses) on row inserts, updates and deletes. As indicated in the oracle's documentation this feature can be used by the application to built a middle tier cache. But this seems to contradict when we have a detailed look on how row ids work.
ROWID's (physical row addresses) can change when various database operations are performed as indicated by this stackoverflow thread. In addition to this, as tom mentions in this thread clustered tables can have same rowids.
Based on the above research, it doesn't seem to be safe to use the rowid sent during the database change notification as the key in the application cache right? This also raises a question on - Should database change notification feature be used to built an application server cache? or is a recommendation made to restart all the application server clusters (to reload/refresh the cache) when the tables of the cached objects undergo any operations which result in rowid's to change? Would that be a good assumption to be made for production environments?
It seems to me to none of operations that can potentially change the ROWID is an operation that would be carried out in a productive environment while the application is running. Furthermore, I've seen a lot of productive software that uses the ROWID accross transaction (usually just for a few seconds or minutes). That software would probably fail before your cache if the ROWID changed. So creating a database cache based on change notification seems reasonable to me. Just provide a small disclaimer regarding the ROWID.
The only somewhat problematic operation is an update causing a movement to another partition. But that's something that rarely happens because it defeats the purpose of the partitioning, at least if it occurred regularly. The designer of a particular database schema will be able to tell you whether such an operation can occur and is relevant for caching. If none of the tables has ENABLE ROW MOVEMENT set, you don't even need to ask the designer.
As to duplicate ROWIDs: ROWIDs aren't unique globally, they are unique within a table. And you are given both the ROWID and the table name in the change notification. So the tuple of ROWID and table name is a perfect unique key for building a reliable cache.
I need some help in auditing in Oracle. We have a database with many tables and we want to be able to audit every change made to any table in any field. So the things we want to have in this audit are:
user who modified
time of change occurred
old value and new value
so we started creating the trigger which was supposed to perform the audit for any table but then had issues...
As I mentioned before we have so many tables and we cannot go creating a trigger per each table. So the idea is creating a master trigger that can behaves dynamically for any table that fires the trigger. I was trying to do it but no lucky at all....it seems that Oracle restricts the trigger environment just for a table which is declared by code and not dynamically like we want to do.
Do you have any idea on how to do this or any other advice for solving this issue?
If you have 10g enterprise edition you should look at Oracle's Fine-Grained Auditing. It is definitely better than rolling your own.
But if you have a lesser version or for some reason FGA is not to your taste, here is how to do it. The key thing is: build a separate audit table for each application table.
I know this is not what you want to hear because it doesn't match the table structure you outlined above. But storing a row with OLD and NEW values for each column affected by an update is a really bad idea:
It doesn't scale ( a single update touching ten columns spawns ten inserts)
What about when you insert a record?
It is a complete pain to assemble the state of a record at any given time
So, have an audit table for each application table, with an identical structure. That means including the CHANGED_TIMESTAMP and CHANGED_USER on the application table, but that is not a bad thing.
Finally, and you know where this is leading, have a trigger on each table which inserts a whole record with just the :NEW values into the audit table. The trigger should fire on INSERT and UPDATE. This gives the complete history, it is easy enough to diff two versions of the record. For a DELETE you will insert an audit record with just the primary key populated and all other columns empty.
Your objection will be that you have too many tables and too many columns to implement all these objects. But it is simple enough to generate the table and trigger DDL statements from the data dictionary (user_tables, user_tab_columns).
You don't need write your own triggers.
Oracle ships with flexible and fine grained audit trail services. Have a look at this document (9i) as a starting point.
(Edit: Here's a link for 10g and 11g versions of the same document.)
You can audit so much that it can be like drinking from the firehose - and that can hurt the server performance at some point, or could leave you with so much audit information that you won't be able to extract meaningful information from it quickly, and/or you could end up eating up lots of disk space. Spend some time thinking about how much audit information you really need, and how long you might need to keep it around. To do so might require starting with a basic configuration, and then tailoring it down after you're able to get a sample of the kind of volume of audit trail data you're actually collecting.
WinXP Pro
Oracle 10g Instant Client 10.2.0.1
MS Access 2003
When I link a table in MS Access, the pick list that appears shows me every table and view in the system I have access to. This list is quite large. Normally, I really only want to look at the tables that I own. Is there a way to filter the items displayed based on owner, or any other criteria?
Not really.
You could work around it by getting another account set up that just has access to your tables and link against them that way. When you are pleased as punch with the links you have created, you can always update the links (link to a new location, pointing at your account perhaps) in the Link Table Manager.
You could create a local table of the objects (tables and views) you 'own' in the distant database. You could then write some VBA code where, by looping on this table and using the doCmd.TransferDatabase method, you could automatically generate your links.
Yes, you can set a SCHEMALIST parameter within your ODBC connection (under the advanced settings tab) and specify the table schemas you want to include in your table link list. This will then bring back only the tables you listed in the SCHEMALIST.