Birth, Death, Infinity Gus Björklund. Progress. Dan Foreman. BravePoint. PUG Challenge Americas,...

Birth, Death, Infinity

Gus Björklund. Progress.

Dan Foreman. BravePoint.PUG Challenge Americas, 9-12 June 2013

who are we ?

Conception

A Table is defined

Use the Data Dictionary Tool

• Type in all the information

Load a "df" file

• run prodict/load_df.p (os-getenv ("SCHEMADIR") + "/" "customer.df").

Execute a SQL DDL statement• CREATE TABLE pub.customer (cust-num integer, . . . ) AREA "a51";

Methods for defining a new table:

Where does the definition go?

Table definitions

_file _field

_field

One _field record (row) for each field (column) of a table

The _* tables live in the Schema Area. Put yours elsewhere.

List Your Tables and Their Fields

output to tables.txt.for each _file where (0 < _file-num):

put _file-name skip. for each _field of _file: put “ “ _field-name skip. end. put “” skip.end.output close.

Index definitions

_file _index _index-field

_index-field

One _index record for each index of a table

One _index-field record for each key component of an index

_index

List indexes and key components by table

output to index.txt.for each _file where (0 < _file-num): put _file-name skip. for each _index of _file: put " " _index-name skip. for each _index-field of _index: find _field where recid (_field) = _field-recid. put " " _field-name skip. end. end. put "" skip.end.output close.

Where do the default values go?

the template record

Each table has a template record

Column values in the template become the default values

Template records NOT stored with schema metadata

• go in table's home area or schema area (v11)

• have to read from database to get template

TODAY and NOW defaults replaced with current values

CREATE a new row in a 4GL program

create customer.

CREATE a new row in a 4GL program

create customer.

what happens?

we read template record from database(if we don't have it already)

client buffer is filled with a copy of the template record

current values inserted for TODAY, NOW

no write to database – db knows nothing about the create at this point.

Where does customer row go?

customer

orderEtc.

CI for customer

FDTBL fordatabase foo

ICB for tablecustomer

row buffer

assign column values

Address Address2 City Contact Curr-bal Cust-num Discount Max-credit Mnth-sales Name

Phone Sales-region Sales-rep St Tax-no Terms Ytd-sls Zip

when do we send it to the database ?

database accelerator

send row to database

client's row buffer

server's networkmessage buffer

server's row buffer

client's networkmessage buffer

TCP/IP

where do we put it ?

Database Pages (Blocks)

Database divided into fixed-size blocks or “pages” Adjacent pages form clusters Different kinds of pages store different kinds of data Disk i/o done in page size units Each page has unique identifier – its “dbkey”

see these slides for space allocation algorithm details

Space, the final frontierhttp://communities.progress.com/pcom/docs/DOC-107729

Find data block, read into database buffer pool

HashTable

LRU Chain “oldest”“newest”

Page Writer Queue

Checkpoint Queue

Update data block

acquire exclusive lock on buffer generate "create" bi note spool bi note copy from row buffer to data block update block free space if needed mark buffer modified release buffer lock

note: simplified.

some details omitted to protect the innocent

Record In A Row Data Block (aka RM Block)

block header

RM block header

dir entry 0

free space

record 0

Newly created row is stored in some row data block and assigned an available directory entry.

The chosen block and directory entry determine the ROWID

record 1record 2

record 3

dir entry 1dir entry 2dir entry 3

Birth Alternatives

Other ways records are born

INSERT INTO customer (cust-no, name street, city, state) VALUES (642, 'gus', '14 oak park', 'bedford', 'ma');

INSERT INTO customer (cust-no, name street, city, state) SELECT . . . FROM . . . WHERE . . . ;

binary load:

proutil foo -C load bar.bd

Possible Problems

Things to consider

When record is sent to database before all the values are assigned, one database operation

• create

becomes several

• create

• update

• etc.

The record expands as more values are assigned

• fragmentation will occur

find customer where cust-num = 3447.

Compiler determines index to use (perhaps cust-num)• R-code has index information• Query used to form equality or range bracket

At runtime, load schema cache into memory Look up the table number (# 3) Find _storage-object records for table #3 (for tenant #t) Look up the index number (# 113) Find _storage-object records for index #113 (for tenant #t) Load into “om cache” so we can use again (set -omsize) Get location of index root block from _storage-object Traverse index b-tree to leaf, perhaps cust-num = 3447 Get row's rowid 9006 from index leaf block Get share lock on row 9006 Read data block(s) containing row fragments Copy row fragments to 4GL buffer or network buffer

Find row in database

Block’s DBKEY Type Chain Backup Ctr

Next DBKEY in Chain Block Update Counter

Free SpaceFree

Dirs.Rec 0 Offset Rec 1 Offset

Rec 2 Offset Rec n Offset

Free Space

Used Data Space

Record 0

Record 2

Record 1

server’s row buffer

Share locked RM block in buffer pool

client’s networkmessage buffer

client's row buffer

server’s networkmessage buffer

TCP/IP

row buffer connected

customer

orderEtc.

CI for customer

FDTBL fordatabase foo

ICB for tablecustomer

row buffer (cust 3447)

UPDATES

do transaction:

find customer where cust-num = 3447 exclusive-lock:

customer.city = "Westford".

end.end.

Assign new value to city

“Westford”

4GL runtime stack

row buffer (cust 3447)

Boston

ICB for table customer

CI for customer

field n

Assign new value to city

“Westford”

4GL runtime stack

row buffer

Westford

ICB for table customer

CI for customer

field n

when do we send it to the database ?

send row to database

client's row buffer

server's networkmessage buffer

server's row buffer

client's networkmessage buffer

TCP/IP

Update data block

Acquire exclusive lock block buffer

read data block into buffer pool

generate "record difference" bi note

spool bi note

modify data block

update free space

mark block modified

release buffer lock

Update other data blocks

Indexes have to be updated too (city is a key field)

delete existing index entry for "Boston"

insert new index entry for "Westford"

Fragment chain

block header

RM block header

dir entry 0

free space

record 0record 1record 2

record 3(part 1 of row)

block header

RM block header

dir entry 0

free space

record 0record 1 (part 2 of row)

dir entry 1

Deleting

do transaction:

for each customerwhere city = "Boston":

delete customer.

end.end.

Deleting (sql)

delete from customer where city = "Boston";

Update data block

Acquire exclusive lock block buffer

read data block into buffer pool

generate "record delete" bi note

spool bi note

modify data block

update free space

mark block modified

release buffer lock

Update other data blocks

Indexes have to be updated too

After each record delete

• delete existing index entry for "Boston"

• delete all the other index entries too

For unique index entries, replace with a reservation (placeholder)

• the key value cannot be used until deleting transaction commits

deleted ROWID Reservation

block header

RM block header

dir entry 0

free space

ROWID cannot be recycled until after the deleting transaction commits.

block header

RM block header

dir entry 0

free space

What ELSE can go wrong during UNDO ?

What could go wrong ?

block header

RM block header

dir entry 0

free space

What ELSE can go wrong during UNDO ?

block header

RM block header

dir entry 0

free space

record 0record 1

record 2

What can go wrong during UNDO ?

Not enough space. another transaction has taken it.

Infinity

How can a row live after death ?

Life after death

Your records live on forever in:

• Backup archives

• Archived after-image extents

• Audit data

• Archived audit data

• Binary dump files

• Reports

• Dropbox

• etc.

If you have any of these, where? Can you find a specific record?

Are the data encrypted? Where are the keys ?

Can we subpeona your records ? We may.

That’s all we have time for today, except

Answersemail:

gus@progress.com

danf@prodb.com

Birth, Death, Infinity Gus Björklund. Progress. Dan Foreman. BravePoint. PUG Challenge Americas,...

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