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system calls requires that the calling convention adopted by the operating system is implemented, and it is often used to interact with different runtimes Another popular approach is to support the calling convention adopted by C compilers because it is widely used and has become a fairly universal language for interoperability Note that although many operating systems are implemented in C, the libraries providing system calls may adopt different calling conventions This is the case of Microsoft Windows where the operating system adopts the so-called stdcall calling convention rather than the C calling convention A significant dimension in the arena of possible calling conventions is the responsibility for removing the activation record from the thread stack At first glance, it may seem obvious that it is the called function that before returning resets the stack pointer to the previous state.

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Run1 latches total versus runs -- difference and pct Run1 Run2 Diff Pct 149,837 223,287 73,450 67.11%

Now, these two simulations ran in about the same amount of time by the CPU clock. The material difference to note, however, is the large reduction in cache buffers chains latches. The first implementation (hashed) used significantly fewer, meaning the hashed implementation should scale better in a read-intensive environment, since it needs fewer resources that require some level of serialization. This was due entirely to the fact that the I/O needed by the hashed implementation was significantly reduced over the HEAP table you can see the statistic consistent gets in that report bears this out. The TKPROF shows it even more clearly: SELECT * FROM T_HASHED WHERE OBJECT_ID = :B1 call count ------- -----Parse 1 Execute 72081 Fetch 72081 ------- -----total 144163 cpu elapsed disk query current -------- ---------- ---------- ---------- ---------0.00 0.00 0 0 0 10.20 10.36 0 2 0 1.73 1.69 0 72081 0 -------- ---------- ---------- ---------- ---------11.94 12.06 0 72083 0 rows ---------0 0 72081 ---------72081

This is not the case for programming languages such as C that allow functions with a variable number of arguments such as printf When variable arguments are allowed, it is the caller that knows exactly the size of the activation record; therefore, it is its responsibility to free the stack at the end of the function call Apart from being consistent with the chosen convention, it may seem that there is little difference between the two choices, but if the caller is responsible for cleaning the stack, each function invocation requires more instructions, which leads to larger executables; for this reason, Windows uses the stdcall calling convention instead of the C calling convention.

Rows Row Source Operation ------- --------------------------------------------------1 TABLE ACCESS HASH T_HASHED (cr=1 pr=0 pw=0 time=0 us) ******************************************************************************** SELECT * FROM T_HEAP WHERE OBJECT_ID = :B1 call count ------- -----Parse 1 Execute 72080 Fetch 72080 ------- -----total 144161 Rows ------1 1 cpu elapsed disk query current -------- ---------- ---------- ---------- ---------0.00 0.00 0 0 0 10.55 10.84 0 0 0 1.80 1.85 0 216240 0 -------- ---------- ---------- ---------- ---------12.36 12.70 0 216240 0 rows ---------0 0 72080 ---------72080

It is important to notice that the CLR uses an array of objects to pass a variable number of arguments, which is very different from the variable arguments of C because the method receives a single pointer to the array that resides in the heap It is important to note that if the memory layout of the activation record is compatible, as it is in Windows, the use of the cdecl convention instead of the stdcall convention leads to a subtle memory leak If the runtime assumes the stdcall convention (that is the default) and the callee assumes the cdecl convention, the arguments pushed on the stack are not freed, and at each invocation the height of the stack grows until a stack overflow happens The CLR supports a number of calling conventions.

Row Source Operation --------------------------------------------------TABLE ACCESS BY INDEX ROWID T_HEAP (cr=3 pr=0 pw=0 time=0 us cost=2 si ) INDEX UNIQUE SCAN T_HEAP_PK (cr=2 pr=0 pw=0 time=0 us cost=1 size=0 )