Getting Started with DB2 Express-C

Chapter 12 – Maintenance Tasks 207
Example:
RUNSTATS ON TABLE myschema.employee
12.1.3 BIND / REBIND
After successfully running a RUNSTATS command, not all queries will use the latest
statistics. Static SQL access plans are determined when you first issue a BIND command,
so the statistics used at that time may not be the same as the current ones. Figure 12.2
helps illustrate this idea.
Figure 12.2 – Static SQL bind process
In Figure 12.2 an embedded C program (stored as a file with a “sqc” extension) is
precompiled. After pre-compilation, two files are generated, a “.c” file containing the C code
with all the SQL commented out; and a “.bnd” file containing all the SQL statements. The C
file with the “.c” extension is compiled as usual with a C compiler, creating a “library” as
shown in the top right hand side of the figure. The “.bnd” file is similarly bound, generating
a package that is stored in the database. Binding is equivalent to compiling the SQL
statements where the best access plan is determined based on the statistics available at
the time, and then storing them in the package.
Now, what happens if 1 million rows are inserted into a table used in the SQL for this
embedded C program? After the insertion, if a RUNSTATS is performed, the statistics will
be updated; however the package will not be automatically updated to recalculate the
access path based on the latest statistics. The db2rbind command can be used to rebind
all the existing packages to take into account the latest stats.
Syntax:
db2rbind database_alias -l