I have been thinking about an issue of speed versus readability lately. Which one prevails over the other. I have a case statement and a loop which positions can be interchanged to come to the same result.<\/p>\n
<\/p>\n
Consider these two implementations:<\/p>\n
DECLARE<\/span>\n caseexpr <\/span>PLS_INTEGER<\/span>;\n var <\/span>NUMBER<\/span>;\n starttime <\/span>pls_integer<\/span>;\n endtime <\/span>pls_integer<\/span>;\n<\/span>BEGIN<\/span>\n caseexpr :<\/span>=<\/span> <\/span>1<\/span>;\n var :<\/span>=<\/span> <\/span>0<\/span>;\n <\/span>FOR<\/span> idx <\/span>IN<\/span> <\/span>1<\/span> .. <\/span>10000000<\/span> <\/span>LOOP<\/span>\n <\/span>CASE<\/span> caseexpr\n <\/span>WHEN<\/span> <\/span>1<\/span> <\/span>THEN<\/span>\n var :<\/span>=<\/span> var <\/span>+<\/span> <\/span>1<\/span>;\n <\/span>WHEN<\/span> <\/span>2<\/span> <\/span>THEN<\/span>\n var :<\/span>=<\/span> var <\/span>+<\/span> <\/span>2<\/span>;\n <\/span>WHEN<\/span> <\/span>3<\/span> <\/span>THEN<\/span>\n var :<\/span>=<\/span> var <\/span>+<\/span> <\/span>3<\/span>;\n <\/span>WHEN<\/span> <\/span>4<\/span> <\/span>THEN<\/span>\n var :<\/span>=<\/span> var <\/span>+<\/span> <\/span>4<\/span>;\n <\/span>END<\/span> <\/span>CASE<\/span>;\n <\/span>END<\/span> <\/span>LOOP<\/span>;\n DBMS_OUTPUT.PUT_LINE(to_char(var));\n<\/span>END<\/span>;\n<\/span>\/<\/span>\n<\/span><\/div><\/pre>\n<\/div>\n
<\/p>\n
\nDECLARE<\/span>\n caseexpr <\/span>PLS_INTEGER<\/span>;\n var <\/span>NUMBER<\/span>;\n<\/span>BEGIN<\/span>\n caseexpr :<\/span>=<\/span> <\/span>1<\/span>;\n var :<\/span>=<\/span> <\/span>0<\/span>;\n <\/span>CASE<\/span> caseexpr\n <\/span>WHEN<\/span> <\/span>1<\/span> <\/span>THEN<\/span>\n <\/span>FOR<\/span> idx <\/span>IN<\/span> <\/span>1<\/span> .. <\/span>10000000<\/span> <\/span>LOOP<\/span>\n var :<\/span>=<\/span> var <\/span>+<\/span> <\/span>1<\/span>;\n <\/span>END<\/span> <\/span>LOOP<\/span>;\n <\/span>WHEN<\/span> <\/span>2<\/span> <\/span>THEN<\/span>\n <\/span>FOR<\/span> idx <\/span>IN<\/span> <\/span>1<\/span> .. <\/span>10000000<\/span> <\/span>LOOP<\/span>\n var :<\/span>=<\/span> var <\/span>+<\/span> <\/span>2<\/span>;\n <\/span>END<\/span> <\/span>LOOP<\/span>;\n <\/span>WHEN<\/span> <\/span>3<\/span> <\/span>THEN<\/span>\n <\/span>FOR<\/span> idx <\/span>IN<\/span> <\/span>1<\/span> .. <\/span>10000000<\/span> <\/span>LOOP<\/span>\n var :<\/span>=<\/span> var <\/span>+<\/span> <\/span>3<\/span>;\n <\/span>END<\/span> <\/span>LOOP<\/span>;\n <\/span>WHEN<\/span> <\/span>4<\/span> <\/span>THEN<\/span>\n <\/span>FOR<\/span> idx <\/span>IN<\/span> <\/span>1<\/span> .. <\/span>10000000<\/span> <\/span>LOOP<\/span>\n var :<\/span>=<\/span> var <\/span>+<\/span> <\/span>4<\/span>;\n <\/span>END<\/span> <\/span>LOOP<\/span>;\n <\/span>END<\/span> <\/span>CASE<\/span>;\n DBMS_OUTPUT.PUT_LINE(to_char(var));\n<\/span>END<\/span>;\n<\/span><\/div><\/pre>\n<\/div>\n<\/p>\n
The first on has one (1) loop in which the case expression is evaluated a lot of times. The second has one (1) case expression which holds a loop for every possible case.<\/p>\n
When I ran and timed these snippets (using SELECT to_char(systimestamp, ‘SS:FF6’) FROM dual; before and after the snippets) on both Oracle 11G and Oracle 9i, it appeared the second one performed a little bit faster than the first one. I had to have the loop run 10000000 times to see a little difference, less than half a second, but the second one was a bit faster.<\/p>\n
But when it comes to readability, I think the first one wins. This also goes for the maintainability. What if I want to change the loop. The first one just needs a change in one line, the second one needs changes in every case branch.<\/p>\n
Seeing that the differences are so tiny, I think I will choose the first option as my implementation, since this is more readable and better maintainable.<\/p>\n","protected":false},"excerpt":{"rendered":"
I have been thinking about an issue of speed versus readability lately. Which one prevails over the other. I have a case statement and a loop which positions can be interchanged to come to the same result.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2,5],"tags":[],"class_list":["post-202","post","type-post","status-publish","format-standard","hentry","category-oracle","category-plsql"],"_links":{"self":[{"href":"https:\/\/blog.bar-solutions.com\/index.php?rest_route=\/wp\/v2\/posts\/202","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.bar-solutions.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.bar-solutions.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.bar-solutions.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.bar-solutions.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=202"}],"version-history":[{"count":0,"href":"https:\/\/blog.bar-solutions.com\/index.php?rest_route=\/wp\/v2\/posts\/202\/revisions"}],"wp:attachment":[{"href":"https:\/\/blog.bar-solutions.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=202"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.bar-solutions.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=202"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.bar-solutions.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=202"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}