SQL Anywhere Tips and Tricks

(c) 2015 Independent SAP TechnicalAnnual Conference, 2015
SQL AnywhereTipsandTricks
Jason Hinsperger
Product Manager, SAP

SQL AnywhereTipsandTricks
Autocommit
C External Environments
Dedicated Tasks
sp_list_directory and friends
Variables in USING and AT clauses

AUTOCOMMIT

Autocommit
Autocommit Off Chained
On
Autocommit On Chained
Off
IT DEPENDS!
For TDS connections Autocommit on/off is effectively equivalent to
Chained off/on
 jConnect, Open Client
For other connections, Autocommit and Chained are completely
different
 ODBC, SQLA JDBC, .NET, …
Chained mode controls whether the server does a commit after each
statement

Autocommit VSChained(ODBC Example)
 CREATE PROCEDURE p( IN id INT, OUT numrows INT )
 BEGIN
 SAVEPOINT sv;
 INSERT INTO tab2 SELECT * FROM tab1 WHERE tab1.tabid < id;
 SELECT count(*) INTO numrows FROM tab2;
 ROLLBACK TO SAVEPOINT sv;
 END
If Autocommit is ON (driver default) and Chained is OFF (database
default), then executing the above procedure via ODBC does not
change the contents of tab2
If Autocommit is either ON or OFF and Chained is ON, then executing the
above procedure via ODBC does change the contents of tab2 AND will
generate an error

TurningAutocommit Off
So when we say “turn autocommit off” we actually mean make the API
call on the client
 ODBC: SQLSetConnectAttr( … SQL_ATTR_AUTOCOMMIT … )
 JDBC: Connection.setAutoCommit( false ) (regardless of whether you
are using jConnect or SQLA JDBC)
 …
AND avoid messing with chained mode

C EXTERNAL ENVIRONMENTS

C External EnvironmentsvsIn Process
External StoredProcedures
SQL Anywhere has had the ability to load user provided dlls and shared
objects for a long time
More recently these dlls and shared objects can now be loaded and
executed outside of the server using C External Environments
Loading these dlls and shared objects outside of the server provides:
 Improved server stability
 Greater security of data
 Mixing and matching of server and dll/shared object bitness
 The ability to return result sets from the external stored procedure
 The ability to make server side calls via ODBC or ESQL
 Easier debugging of external dll/shared object

C External EnvironmentsvsIn Process
Changing an external stored procedure from in process to out of process
is as simple as adding a LANGUAGE clause
 CREATE PROCEDURE myextproc(…) EXTERNAL NAME
‘MyExternalProc@myprocs.dll’
 CREATE PROCEDURE myextproc(…) EXTERNAL NAME
‘MyExternalProc@myprocs.dll’ LANGUAGE C_ODBC64
EXTERNAL NAME clause can contain both Unix and Windows definitions
– exactly the same as the in process EXTERNAL NAME clause

C External Environments- DEMO

C External EnvironmentsvsIn-Process
Things to take into consideration when deciding to load dlls and shared
object in C External Environment:
 Time required to make a call out of process is significantly greater than
making an in process call
 Machine resource utilization is higher due to separate process per
connection
 Sharing of data across connections is not allowed

DEDICATED TASKS

Scenario
I have a large number of users who hammer away at my server
throughout the day
Of these users, I have a couple of admin users who get in earlier than
the rest and who must be given priority when they make server
requests
The response time for my admin users decreases significantly when the
rest of the users get in and start making constant server requests
How can I fix it so that my admin users are always given priority over
the other users
I am not as concerned about the response time for requests from my
non-admin users

Dedicatedtasks
One way to solve this problem is to assigned dedicated server tasks to
the admin users
This is done using the dedicated_task database option
The admin users could be assigned a login procedure that automatically
sets the dedicated_task option to on for that connection
Or the admin users could be given permission to set and unset the
option on the fly as needed

DedicatedTasks- DEMO

Dedicatedtasks
Note that dedicating a server task to a connection reduces the number
of server tasks available for servicing requests from other connections
This task cannot be used by the server for another connection EVEN IF
the connection that the task is dedicated to is not currently executing
a request in the server
This feature should therefore be used with caution to avoid starvation of
requests
However for those unique situations where a request absolutely must
make it into the server; the dedicated_task option can be very useful

SP_LIST_DIRECTORY AND
FRIENDS

Preamble: DirectoryAccessServers
sp_list_directory() and friends can be used as a light weight replacement
for directory access servers
Directory access servers allow applications to create proxy tables for
“querying” and manipulating directories on the server machine
 CREATE SERVER … CLASS ‘directory’ USING ‘root=…;subdirs=…’
Some people find that directory access servers are cumbersome and too
powerful for what they really want to do

sp_list_directoryandfriends
To provide an alternate approach to querying and managing directories
on server machines, we added a set of file and directory stored
procedures





Combined with xp_read_file() and xp_write_file(), this full set of stored
procedures can provide the same functionality as directory access
servers without requiring the creation of remote servers and extern
logins

Directory procedures File procedures
dbo.sp_list_directory()
dbo.sp_copy_directory() dbo.sp_copy_file()
dbo.sp_move_directory() dbo.sp_move_file()
dbo.sp_delete_directory() dbo.sp_delete_file()

sp_list_directoryandfriends- DEMO

sp_list_directoryandfriends– final
thoughts
In some ways, sp_list_directory() and friends are more efficient than
directory access servers
They are also easier to use and do not require any setup
Their use can also be easily restricted via system privileges and secure
features
However, directory access servers have certain optimizations that do
not currently exist with sp_list_directory() and friends
 Select … from dirtab where file_name=‘…’
 Select … from dirtab where left(file_name, …) = ‘…’
But if all you want to do is list the contents of a directory, fetch some
files or do some directory or file administration, sp_list_directory() and
friends will usually provide the better alternative


VARIABLESIN ‘USING’ AND
‘AT’ CLAUSES

Preamble: Driver = SQL AnywhereNative
When creating DSN-less remote servers to another SQL Anywhere
server, use Driver=SQL Anywhere Native instead of Driver=SQL
Anywhere 16
 eg. CREATE SERVER rem CLASS ‘saodbc’ USING ‘Driver=SQL Anywhere
Native;host=…’

“Driver=SQL AnywhereNative” works on all platforms that support RDA
 Database can be moved from machine to machine and across platforms without requiring changes to the
remote server definition
 ODBC Driver must be available on the machine but does not need to be registered
 Server bypasses ODBC Driver Manager and loads the ODBC Driver directly
 Bypassing ODBC Driver Manager gives a moderate (10%) perf. improvement
 If multiple copies of the ODBC Driver are installed, then the server will pick the first one it finds (usually
that is the one that was installed with that version of the server)

Preamble: ExternLogins
1. When making a remote server connection, SQLA will first attempt to
use EXTERNLOGIN credentials of the current executing user
2. If there are no EXTERNLOGIN credentials of the current executing
user, then SQLA will fail if the current executing user is not the the
current logged in user
3. If the current executing user is the same as the current logged in user
and there are no EXTERNLOGIN credentials for the current logged
in user, then SQLA will attempt to use the local credentials of the
current logged in user
These credentials are appended to the connection string that is sent to
the underlying driver; hence any userid or password values in either
the DSN or the USING clause will get overridden
 CREATE SERVER … USING ‘Driver=SQL Anywhere Native;
…;uid=…;pwd=…’ will not work because driver sees two sets of uid=

Preamble: ExternLogins
Trick: To fool SQL Anywhere into NOT appending uid= and pwd= and
instead using the uid= and pwd= in either the USING clause or the
DSN; create a dummy EXTERN LOGIN with no remote login

CREATE EXTERNLOGIN myuser TO myserver
 Creates an externlogin for myuser to server myserver with no remote login/password
 SQLA will see this externlogin and assume myuser has no remote userid/password for server myserver
 As a result, SQLA will not append any uid= or pwd= when making
a connection to myserver IF the current effective user is myuser
 This allows the driver to use the uid/pwd that is in the USING clause or the DSN

Preamble: USING andAT Clauses
CREATE SERVER … CLASS ‘…’ USING ‘…’
CREATE EXISTING TABLE … AT ‘…’
CREATE PROCEDURE … AT ‘…’
CREATE FUNCTION … AT ‘..’
AT clauses are sometimes also called LOCATION clauses

Trick: CREATE TABLE table-name ( column-list ) AT ‘…’ will create both the
proxy table and the remote table at the same time

Variablesin USING andAT Clauses
 The USING and AT clauses can contain substitution variables which
get evaluated at run time
 These variables take the form {variable-name} and can appear
anywhere
 Variables in the USING and AT clause can be used to redefine or
change the remote server definition or proxy table/procedure
location on the fly
 This can be extremely useful if you have multiple remote servers,
remote tables or remote procedures that you need to manage but
do not want to have to set up individual remote server definitions,
proxy table and/or proxy procedure definitions
 Variables in USING and AT clauses can be used with any remote
server and is not restricted to SQL Anywhere back ends

Variablesin USING andAT Clauses-
DEMO

Final Thoughts
The features presented here are only some of the lesser known but
extremely useful features in SQL Anywhere
A few other such features are:
 Scripting external environments (PERL and PHP)
 TRY … CATCH
 dbo.sp_forward_to_remote_server()
 Sandboxing
 MERGE
 Secure features
 …
All of the features presented here and many more are available today

Final Thoughts
Let us know about your favorite SQL Anywhere feature and how you use
it
 http://scn.sap.com/community/sql-anywhere

Get involved in the SQL Anywhere forum:
 http://sqlanywhere-forum.sap.com

Thank you
Jason Hinsperger
jason.hinsperger@sap.com

SQL Anywhere Tips and Tricks

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