Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

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■SETTING UP YOUR ENVIRONMENT xxxi Runstats Runstats is a tool I developed to compare two different methods of doing the same thing and show which one is superior. You supply the two different methods and runstats does the rest. Runstats simply measures three key things: • Wall clock or elapsed time: This is useful to know, but it isn’t the most important piece of information. • System statistics: This shows, side by side, how many times each approach did something (e.g., a parse call) and the difference between the two. • Latching: This is the key output of this report. As you’ll see in this book, latches are a type of lightweight lock. Locks are serialization devices. Serialization devices inhibit concurrency. Applications that inhibit concurrency are less scalable, can support fewer users, and require more resources. Our goal is always to build applications that have the potential to scale—ones that can service 1 user as well as 1,000 or 10,000 users. The less latching we incur in our approaches, the better off we will be. I might choose an approach that takes longer to run on the wall clock but that uses 10 percent of the latches. I know that the approach that uses fewer latches will scale substantially better than the approach that uses more latches. Runstats is best used in isolation—that is, on a single-user database. We will be measuring statistics and latching (locking) activity that result from our approaches. We do not want other sessions to contribute to the system’s load or latching while this is going on. A small test database is perfect for these sorts of tests. I frequently use my desktop PC or laptop, for example. ■Note I believe all developers should have a test bed database they control to try ideas on, without needing to ask a DBA to do something all of the time. Developers definitely should have a database on their desktop, given that the licensing for the personal developer version is simply “Use it to develop and test with, do not deploy, and you can just have it.” This way, there is nothing to lose! Also, I’ve taken some informal polls at conferences and seminars and discovered that virtually every DBA out there started as a developer. The experience and training developers could get by having their own database—being able to see how it really works—pays large dividends in the long run. To use runstats, you need to set up access to several V$ views, create a table to hold the statistics, and create the runstats package. You will need access to three V$ tables (those magic dynamic performance tables): V$STATNAME, V$MYSTAT, and V$LATCH. Here is a view I use: create or replace view stats as select 'STAT...' || a.name name, b.value from v$statname a, v$mystat b where a.statistic# = b.statistic# union all select 'LATCH.' || name, gets from v$latch;
xxxii ■SETTING UP YOUR ENVIRONMENT Either you can have SELECT on V$STATNAME, V$MYSTAT, and V$LATCH granted directly to you (that way you can create the view yourself), or you can have someone that does have SELECT on those objects create the view for you and grant SELECT privileges to you. Once you have that set up, all you need is a small table to collect the statistics: create global temporary table run_stats ( runid varchar2(15), name varchar2(80), value int ) on commit preserve rows; Last, you need to create the package that is runstats. It contains three simple API calls: • RS_START (runstats start) to be called at the beginning of a runstats test • RS_MIDDLE to be called in the middle, as you might have guessed • RS_STOP to finish off and print the report The specification is as follows: ops$tkyte@ORA920> create or replace package runstats_pkg 2 as 3 procedure rs_start; 4 procedure rs_middle; 5 procedure rs_stop( p_difference_threshold in number default 0 ); 6 end; 7 / Package created. The parameter P_DIFFERENCE_THRESHOLD is used to control the amount of data printed at the end. Runstats collects statistics and latching information for each run, and then prints a report of how much of a resource each test (each approach) used and the difference between them. You can use this input parameter to see only the statistics and latches that had a difference greater than this number. By default this is zero, and you see all of the outputs. Next, we’ll look at the package body procedure by procedure. The package begins with some global variables. These will be used to record the elapsed times for our runs: ops$tkyte@ORA920> create or replace package body runstats_pkg 2 as 3 4 g_start number; 5 g_run1 number; 6 g_run2 number; 7 Next is the RS_START routine. This will simply clear out our statistics-holding table and then populate it with the “before” statistics and latches. It will then capture the current timer value, a clock of sorts that we can use to compute elapsed times in hundredths of seconds:
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