Birth, Death, Infinity
Gus Björklund. Progress.
Dan Foreman. BravePoint.PUG Challenge Americas, 9-12 June 2013
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who are we ?
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Conception
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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?
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Table definitions
_file _field
_field
_field
_field
_field
One _field record (row) for each field (column) of a table
The _* tables live in the Schema Area. Put yours elsewhere.
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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.
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Index definitions
_file _index _index-field
_index-field
_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
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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?
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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
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Birth
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CREATE a new row in a 4GL program
create customer.
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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.
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Where does customer row go?
CONDB
customer
orderEtc.
DBDES
CI for customer
FDTBL fordatabase foo
ICB for tablecustomer
row buffer
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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 ?
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database accelerator
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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 ?
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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
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Find data block, read into database buffer pool
HashTable
LRU Chain “oldest”“newest”
Page Writer Queue
M MM
M M
M MMM
Checkpoint Queue
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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
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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
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Birth Alternatives
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Other ways records are born
sql:
INSERT INTO customer (cust-no, name street, city, state) VALUES (642, 'gus', '14 oak park', 'bedford', 'ma');
sql:
INSERT INTO customer (cust-no, name street, city, state) SELECT . . . FROM . . . WHERE . . . ;
binary load:
proutil foo -C load bar.bd
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Possible Problems
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Things to consider
When record is sent to database before all the values are assigned, one database operation
• create
becomes several
• create
• update
• update
• etc.
The record expands as more values are assigned
• fragmentation will occur
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Life
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READ
find customer where cust-num = 3447.
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READ
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
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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
Num
Dirs.
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
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row buffer connected
CONDB
customer
orderEtc.
DBDES
CI for customer
FDTBL fordatabase foo
ICB for tablecustomer
row buffer (cust 3447)
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UPDATES
do transaction:
find customer where cust-num = 3447 exclusive-lock:
customer.city = "Westford".
end.end.
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Assign new value to city
“Westford”
4GL runtime stack
row buffer (cust 3447)
Boston
ICB for table customer
CI for customer
field n
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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 ?
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send row to database
client's row buffer
server's networkmessage buffer
server's row buffer
client's networkmessage buffer
TCP/IP
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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
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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"
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Fragment chain
block header
RM block header
dir entry 0
free space
record 0record 1record 2
record 3(part 1 of row)
dir entry 1dir entry 2dir entry 3
block header
RM block header
dir entry 0
free space
record 0record 1 (part 2 of row)
dir entry 1
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Death
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Deleting
do transaction:
for each customerwhere city = "Boston":
delete customer.
end.end.
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Deleting (sql)
delete from customer where city = "Boston";
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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
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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
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deleted ROWID Reservation
block header
RM block header
dir entry 0
free space
record 0record 1record 2
dir entry 1dir entry 2dir entry 3
ROWID cannot be recycled until after the deleting transaction commits.
Why ?
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deleted ROWID Reservation
block header
RM block header
dir entry 0
free space
record 0record 1record 2
dir entry 1dir entry 2dir entry 3
ROWID cannot be recycled until after the deleting transaction commits.
Why ?
What ELSE can go wrong during UNDO ?
What could go wrong ?
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deleted ROWID Reservation
block header
RM block header
dir entry 0
free space
record 0record 1record 2
dir entry 1dir entry 2dir entry 3
ROWID cannot be recycled until after the deleting transaction commits.
Why ?
What ELSE can go wrong during UNDO ?
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deleted ROWID Reservation
block header
RM block header
dir entry 0
free space
record 0record 1
record 2
dir entry 1dir entry 2dir entry 3
ROWID cannot be recycled until after the deleting transaction commits.
Why ?
What can go wrong during UNDO ?
Not enough space. another transaction has taken it.
Infinity
How can a row live after death ?
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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.
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That’s all we have time for today, except
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Answersemail: