Firebird Tour 2013: detailed schedule for seminar “All About Transactions”

Firebird Tour 2013: seminar “All About Transactions”

Siegburg, November 22, Kranz Park Hotel

Prague, November 25, Hotel Extol Inn

Overview

#	Topic	Speaker	Time
1	Overview of Firebird development	Vlad Khorsun	30
2	Overview of transactions concept and its parameters.  Examples of transactions parameters and their usage.	Alexey Kovyazin/Pavel Cizar	45
3	Transaction in Firebird: peculiarities and special parameters.  Transaction inventory page, versions and how transactions work in multi-generation database.	Dmitry Kuzmenko	60
	Coffee-Break		15
4	Inside Firebird transactions: what happen inside engine during transactions’ start, commit, rollback. What is retaining, autocommit, how transactions work with GTT. Memory consumption for transactions processing.	Vlad Khorsun	60
5	Transactions interaction and best practices for application development. Conflicts between transactions.	Dmitry Kuzmenko	60
	Lunch		60
6	Garbage collection mechanism and sweep in details	Vlad Khorsun	45
7	Transactions management in various drivers (Delphi, .NET, Java, etc): parameters and approaches.	Dmitry Kuzmenko/Jiri Cincura	45
	Coffee-Break		15
8	Diagnosing transaction management problems: most prevalent problems, how to catch and fix them.	Alexey Kovyazin	60
9	Round table		45

Detailed plan

   1.       Overview of Firebird development

a.       New features and details of Firebird development,

b.      Plan for next releases

   2.       Overview of transactions concept and its parameters.  Examples of transactions parameters and their usage.

a.       Historical overview of transactions: locking engines, dirty read, why Firebird has only snapshot и read_committed

b.      Transaction as logical operation: bridge between business logic and database implementation

c.       What is ACID

d.      Isolation levels: standard levels and Firebird levels

e.      read only\write

f.        wait and nowait

g.       Examples of transactions with various isolation levels, read-only/write and wait/nowait, from the client point of view

   3.       Transaction in Firebird: peculiarities and special parameters.  Transaction inventory page, versions and how transactions work in multi-generation database.

a.       Full syntax of SET TRANSACTION and TPB parameters

b.      Some undocumented parameters

c.       Who create transactions

                                                               i.      Application

                                                             ii.      System transaction (tx #0)

                                                            iii.      Garbage collector

                                                           iv.      Autonomous transactions

                                                             v.      Triggers ON CONNECT\ON DISCONNECT

d.      Versioning basics

e.      How versions are being created

f.        States of transaction in Firebird (active, committed, rolled back, limbo)

g.       Visibility of record versions in transactions

h.      Key differences between Read Committed and Snapshot

i.         Triggers for transactions start and stop

j.        Context variables at transaction’s level

k.       GTT and read-only transactions

   4.    Inside Firebird transactions: what happen inside engine during transactions’ start, commit, rollback.

a.       What happens at transactions’ start

                                                               i.      Global transaction markers (OAT, OST, OIT) and their meaning

                                                             ii.      Autosweep

b.      What happens at transaction commit

                                                               i.      How DWF works

                                                             ii.      DDL queries

                                                            iii.      Dispatching events

                                                           iv.      Flush of dirty pages

                                                             v.      TIP processing

c.       What happens at rollback

                                                               i.      Standard rollback with cache flush

                                                             ii.      Forces rollback without cache flush

                                                            iii.      Rollback transactions with undo-log

                                                           iv.      Rollback without undo-log

d.      What is retaining

e.      Auto-commit (does anybody know about it?)

f.        Managing memory for transactions

                                                               i.      Temporary BLOBs

                                                             ii.      Undo-log

g.       Local TIP and related issues

   5.       Transactions interaction and best practices for application development. Conflicts between transactions.

a.       Transactions interactions types

b.      Templates for transaction usage in application development

c.       Scenarios breakdown: Readers and Readers, Readers and Writers, Writers and Writers

d.      Best practices

                                                               i.      Dictionaries

                                                             ii.      Splitting read and write transactions

                                                            iii.      Locking record with empty Update

                                                           iv.      Locking with SELECT WITH LOCK

                                                             v.      Reports

                                                           vi.      Serialization: how to build effective queues

   6.    Garbage collection mechanism and sweep in details       

a.       Why we need sweep?

b.      How sweep works

c.       Types of the sweep: cooperative, background, background

d.      Differences between sweep and garbage collection

e.      Autosweep: pro and contras

f.        Examples of application design mistakes which lead to excessive garbage

   7.   Transactions management in various drivers (Delphi, .NET, Java, etc): parameters and approaches.

a.       What are direct and non-direct client drivers?

b.      BDE, dbExpress, ODBC, .Net

c.       IBX, FIBPlus, FireDAC

d.      Transactions management in applications: examples

e.      How to manage transactions lifetime in various drivers

f.        How to implement edit dialogs in the effective and safe way

g.       Commit retaining

   8.   Diagnosing transaction management problems: most prevalent problems, how to catch and fix them.

a.       What we can see at gstat -h

b.      OIT, OST, OAT, NEXT  - their combinations and what they mean

c.       When garbage collection does not work?

d.      Transaction markers dynamics analysis with IBTM. Catching sweep moments.

e.      How to determine quantity of garbage versions

f.        How to find long transactions with MON$ tables

g.       Transactions monitoring with MON$ and TraceAPI.

h.      Legacy applications: workarounds for error in transactions management

   9.   Round table: questions and answers

Answers for 3 transactions questions

So, it's time for the answers.

The question 1 is the easiest:

1.       In some transaction there were 3 inserts made. The third INSERT raises exception. Is it possible to commit this transaction?              

                [ ] yes, [ ] no

Answer is Yes, of course. An ability to commit or rollback transaction does not depend on insert operations which were performed in the frame of transaction. Of course, usually application logic is built in the way to commit only successful set of operations, but it's not a rule. 

The second question is a bit more tricky:

2.       In some table there were 10 records. 3 simultaneous transactions were started and then in each transaction 1 record was inserted. In transaction 3 query SELECT COUNT(*) FROM Table was executed. The result will be:      

[ ] 10, [ ] 11, [ ] 12, [ ] 13

In this question you need to take an account that transactions are not committed. As you know, all changes in the frames of non-committed transaction are visible only inside this transaction, so the answer will be 11.

The third question is devoted to the generators concept of Firebird engine.

3.  Initially we have generator with name id, its value is 10. We have simultaneous transactions A and B. In A executed gen_id(id,1), in B gen_id(id,1). Then A was commited and B was rollbacked. What value is in id?      

                [ ] 10, [ ] 11, [ ]12

Generators (or sequences) work outside the frames of transactions. It means that commit or rollback of transactions does not affect the resulted value - i.e., generator ID will be increased both in A and B, and correct answer is 12.

Did you answer all these questions correctly? I guess so, since they are very easy. 

There are more interesting topics related with transactions. For example, do you know that each database in Firebird has a limit of transactions which can be performed between backup/restore cycles? And, more interesting, that unused transactions occupy space in the database, which is released only after backup/restore, and there could be up to 700Mb of such space in the worst case?

If you are interested, consider to visit Firebird 2013 Tour  seminar "All About Transactions" in Siegburg, Germany, November 22, 2013.

3 questions about transactions every Firebird developer should answer correctly

Hi All,

As you probably know, Firebird Project will have a seminar, devoted to transactions topic, in Siegburg (Germany), November 22, 2013. More details: http://firebirdsql.org/en/firebird-conference-tour-2013/
Many developers think that transactions are straightforward and easy thing to understand and use, so probably there is no reason to devote 1 day seminar to discover transactions mechanism in Firebird in great details. Is it so?
Here I offer 3 simple questions about transactions which every Firebird developer should answer. Please take a look and choose the correct answer:

1.       In some transaction there were 3 inserts made. The third INSERT raises exception. Is it possible to commit this transaction?              

                [ ] yes, [ ] no

2.       In some table there were 10 records. 3 simultaneous transactions were started and then in each transaction 1 record was inserted. In transaction 3 query SELECT COUNT(*) FROM Table was executed. The result will be:      

[ ] 10, [ ] 11, [ ] 12, [ ] 13

3.  Initially we have generator with name id, its value is 10. We have simultaneous transactions A and B. In A executed gen_id(id,1), in B gen_id(id,1). Then A was commited and B was rollbacked. What value is in id?      

                [ ] 10, [ ] 11, [ ]12

So, take your time and choose correct answers. Tomorrow we'll consider the questions and their answers.