{"id":303,"date":"2018-01-15T16:09:11","date_gmt":"2018-01-15T16:09:11","guid":{"rendered":"https:\/\/www.spotonoracle.com\/?p=303"},"modified":"2018-01-15T16:09:11","modified_gmt":"2018-01-15T16:09:11","slug":"play-fetch-get-exactly-one-row-at-a-time","status":"publish","type":"post","link":"https:\/\/www.spotonoracle.com\/?p=303","title":{"rendered":"Play fetch – get exactly one row at a time"},"content":{"rendered":"

Every once in a while I want SQL*Plus to fetch one row at a time, so I set ARRAYSIZE to 1.
\nBut:<\/p>\n

\r\nSQL> set autotrace traceonly statistics\r\nSQL> set arraysize 1\r\nSQL> select * from user1.cf1 where rownum <= 100;\r\n\r\nStatistics\r\n----------------------------------------------------------\r\n          1  recursive calls\r\n          0  db block gets\r\n        102  consistent gets\r\n          0  physical reads\r\n          0  redo size\r\n     258194  bytes sent via SQL*Net to client\r\n       1091  bytes received via SQL*Net from client\r\n         51  SQL*Net roundtrips to\/from client\r\n          0  sorts (memory)\r\n          0  sorts (disk)\r\n        100  rows processed\r\n<\/pre>\n
We only did 51 network round trips to fetch 100 rows. This is because SQL*Plus is using OCI and the default for prefetch (OCI_ATTR_PREFETCH_ROWS) is set to 1. So we end up with 2 rows per fetch call (note that with prefetch 1, the first round trip already returns 1 row).<\/p>\n
Now, I really, really want to fetch just one row at a time. Starting with Oracle 12.1 you can create an OCI configuration file to specify various settings, one of them being prefetch. See documentation<\/a> for more details.<\/p>\n
vi ${TNS_ADMIN}\/oraaccess.xml<\/p>\n
\r\n<?xml version="1.0"?>\r\n <oraaccess xmlns="http:\/\/xmlns.oracle.com\/oci\/oraaccess" xmlns:oci="http:\/\/xmlns.oracle.com\/oci\/oraaccess" schemaLocation="http:\/\/xmlns.oracle.com\/oci\/oraaccess http:\/\/xmlns.oracle.com\/oci\/oraaccess.xsd">\r\n  <default_parameters>\r\n    <prefetch>\r\n      <rows>0<\/rows>\r\n    <\/prefetch>\r\n  <\/default_parameters>\r\n<\/oraaccess>\r\n<\/pre>\n
With this configuration in place we should see 100+ network round trips.<\/p>\n
\r\nSQL> set autotrace traceonly statistics\r\nSQL> set arraysize 1\r\nSQL> select * from user1.cf1 where rownum <= 100;\r\n\r\nStatistics\r\n----------------------------------------------------------\r\n          0  recursive calls\r\n          0  db block gets\r\n        102  consistent gets\r\n          0  physical reads\r\n          0  redo size\r\n     267988  bytes sent via SQL*Net to client\r\n       1652  bytes received via SQL*Net from client\r\n        102  SQL*Net roundtrips to\/from client\r\n          0  sorts (memory)\r\n          0  sorts (disk)\r\n        100  rows processed\r\n<\/pre>\n
Go play fetch \ud83d\ude09<\/p>\n","protected":false},"excerpt":{"rendered":"
Every once in a while I want SQL*Plus to fetch one row at a time, so I set ARRAYSIZE to 1. But: SQL> set autotrace traceonly statistics SQL> set arraysize 1 SQL> select * from user1.cf1 where rownum <= 100; Statistics ———————————————————- 1 recursive calls 0 db block gets 102 consistent gets 0 physical reads […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-303","post","type-post","status-publish","format-standard","hentry","category-general"],"_links":{"self":[{"href":"https:\/\/www.spotonoracle.com\/index.php?rest_route=\/wp\/v2\/posts\/303","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.spotonoracle.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.spotonoracle.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.spotonoracle.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.spotonoracle.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=303"}],"version-history":[{"count":8,"href":"https:\/\/www.spotonoracle.com\/index.php?rest_route=\/wp\/v2\/posts\/303\/revisions"}],"predecessor-version":[{"id":311,"href":"https:\/\/www.spotonoracle.com\/index.php?rest_route=\/wp\/v2\/posts\/303\/revisions\/311"}],"wp:attachment":[{"href":"https:\/\/www.spotonoracle.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=303"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.spotonoracle.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=303"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.spotonoracle.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=303"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}