.NET/ASP.NET/C#/VB.NET PDF Document SDK

The let bindings of the SchemaReader type are effectively a form of precomputation (they can also be seen as a form of compilation)They precompute as much information as possible given the schema For example, the section analyzes the fields of the schema type and computes functions for creating objects of the field types It also computes the permutation from the text file columns to the record fields, using the type Microsoft FSharpCollectionsPermutation 4 The data objects are ultimately constructed using reflection functions, in this case a function computed by MicrosoftFSharpReflectionValueGetRecordConstructor or primitive values parsed using SystemInt32Parse and similar functions This and other functions for creating F# objects dynamically are in the MicrosoftFSharpReflection library Other functions for creating other NET objects dynamically are in the System Reflection library 5.

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concurrency issues. It is my firm belief that autonomous transactions are a feature that Oracle should not have exposed to developers for the simple reason that most developers do not know when and how to use them properly. The improper use of an autonomous transaction can and will lead to logical data-integrity corruption issues. Beyond using them as a demonstration tool, autonomous transactions have exactly one other use as an error-logging mechanism. If you wish to log an error in an exception block, you need to log that error into a table and commit it without committing anything else. That would be a valid use of an autonomous transaction. If you find yourself using an autonomous transaction outside the scope of logging an error or demonstrating a concept, you are almost surely doing something very wrong.

Here, I will use an autonomous transaction in the database to have two concurrent transactions in a single session. An autonomous transaction starts a subtransaction separate and distinct from any already established transaction in the session. The autonomous transaction behaves as if it were in an entirely different session for all intents and purposes, the parent transaction is suspended. The autonomous transaction can be blocked by the parent transaction (as we ll see) and, further, the autonomous transaction can t see uncommitted modifications made by the parent transaction. For example: ops$tkyte%ORA11GR2>>> create table t 2 ( processed_flag varchar2(1) 3 ); Table created. ops$tkyte%ORA11GR2> create bitmap index 2 t_idx on t(processed_flag); Index created. ops$tkyte%ORA11GR2> insert into t values ( 'N' ); 1 row created. ops$tkyte%ORA11GR2> declare 2 pragma autonomous_transaction; 3 begin 4 insert into t values ( 'N' ); 5 commit; 6 end; 7 / declare * ERROR at line 1: ORA-00060: deadlock detected while waiting for resource ORA-06512: at line 4

The member bindings of SchemaReader interpret the residue of the precomputation stage, in this case using the information and computed functions to process the results of splitting the text of a line This technique has many potential applications and has been used for CSV file reading and database schema generation..

Since I used an autonomous transaction and created a subtransaction, I received a deadlock meaning my second insert was blocked by my first insert Had I used two separate sessions, no deadlock would have occurred Instead, the second insert would have just blocked and waited for the first transaction to commit or roll back This symptom is exactly what the project in question was facing the blocking, serialization issue So we had an issue whereby not understanding the database feature (bitmap indexes) and how it worked doomed the database to poor scalability from the start To further compound the problem, there was no reason for the queuing code to ever have been written The database has built-in queuing capabilities and has had them since version 80 of Oracle which was released in 1997.

This built-in queuing feature gives you the ability to have many producers (the sessions that insert the N, the unprocessed records) concurrently put messages into an inbound queue and have many consumers (the sessions that look for N records to process) concurrently receive these messages That is, no special code should have been written in order to implement a queue in the database The developers should have used the built-in feature And they might have, except they were completely unaware of it Fortunately, once this issue was discovered, correcting the problem was easy We did need an index on the processed-flag column, just not a bitmap index We needed a conventional B*Tree index It took a bit of convincing to get one created No one wanted to believe that conventionally indexing a column with two distinct values was a good idea.