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Using five concurrent sessions, we start inserting into this table like wild If we measure the systemwide wait events for block-related waits both before and after inserting, we will find large waits, especially on data blocks (trying to insert data) This is frequently caused by insufficient FREELISTs on tables (and on indexes, but we ll cover that in detail in the next chapter Indexes ) I used Statspack for this I took a statspacksnap, executed a script that started the five concurrent SQL*Plus sessions, and waited for them to exit, before taking another statspacksnap The script these sessions ran was simply: begin for i in 1 . 100000 loop insert into t values ( i, 'x' ); end loop; commit; end; / exit; Now, this is a very simple block of code, and I m the only user in the database here I should get the best possible performance.

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In Kitty, statements can be separated by semicolons. This is handled in the StmtList grammar production whose semantic extract is a list of statements. Note that you could have written this rule in a head-recursive way: StmtList: | Stmt { [$1] } | Stmt SEMI StmtList { $1 @ [ $3 ] } Unlike in recursive-descent or any other LL parsing technique, the previous rule does not pose a problem for fsyacc, and thus no left-factoring is needed. However, it does create a copy of the statement list each time a new expression is appended to it. We have eliminated this by using the following productions: StmtList: | Stmt { [$1] } | StmtList SEMI Stmt { $3 :: $1 } combined with a List.rev where the rule is used. This rule consumes all statements and inserts each one by one to the singleton list that contains the first statement. As a result, the return list will be in reverse order, which is why you need to apply List.rev. You may want to define a separate rule to perform this operation. Another feature that is often needed is the ability to parse empty or optional lists. This can be easily accomplished using an empty (epsilon) symbol as in the following example: StmtListOpt: { [] } | StmtList { $1 } This rule matches an optional list of statements and returns an empty list if no statements can be parsed.

I have plenty of buffer cache configured, my redo logs are sized appropriately, indexes won t be slowing things down, I m running on a machine with two hyperthreaded Xeon CPUs this should run fast What I discovered afterward, however, is the following: Snapshot Snap Id Snap Time Sessions Curs/Sess Comment ~~~~~~~~ ---------- ------------------ -------- --------- -----------------Begin Snap: 364 17-Mar-10 11:58:24 26 17 End Snap: 365 17-Mar-10 11:59:01 24 18 Elapsed: 062 (mins) Av Act Sess: 49 DB time: 304 (mins) DB CPU: 118 (mins) Top 5 Timed Events Avg %Total ~~~~~~~~~~~~~~~~~~ wait Call Event Waits Time (s) (ms) Time ----------------------------------------- ------------ ----------- ------ -----buffer busy waits 199,708 107 1 535 CPU time 70 350 db file async I/O submit 44 11 252 55 log file parallel write 1,130 9 8 45 control file parallel write 56 1 16 .

4 ------------------------------------------------------------I collectively waited 107 seconds, or about 21 seconds per session on average, on buffer busy waits These waits are caused entirely by the fact that there are not enough FREELISTs configured on my table for the type of concurrent activity that is taking place I can eliminate most of that wait time easily, just by creating the table with multiple FREELISTs.