Re: SQL CTE of a UNION kills performance -- MIDRANGE-L

Subject: Re: SQL CTE of a UNION kills performance
From: Buck Calabro <kc2hiz@xxxxxxxxx>
Date: Wed, 29 Aug 2018 11:12:24 -0400
Autocrypt: addr=kc2hiz@xxxxxxxxx; keydata= xsDiBEcbaT4RBADqmM9OgXil65pjrxclJpxuAF6vraI3kkmJbEHb5ElL7EquHE3QDuFqFgIB 4NZLHDbVAh0AD5exAX+r+xg//UvtBc2k34HROnCpWTMnIOaSVhhVjpYEbZGLz6wfrRpu4Qyn 45iaKT4F0qcHo+0LrGQPef3xrFkUhxURgzY5zgo6+wCg/XjYJ155witPWB2CbNf6RAm9QT0D /jSp6YhvE3xPE12aBuRYM678JTbaQfuYv4HUfug1Wz/0zH5btfEihWVN4wbKaoQ/H/29v2TP /Lyh8XTVd3Z0rz4iaSD5fGicn81WPANBeIepLB8vpfEik6UhHpN1DJkz6Ryw2mgx8p53LhHV Ck4Jt0HP2TAl3f7QTXGFOiFzJwEqBACsHk/gFpKAHdv7n4vJoHqp0RNgOOyhnTThlulPilt6 tAaSe10FOrrugBuLMn7wXBANQ1ApmIb5yNjhYqPREj65OVv2MUbw8H2HnQs//Z6aodyR/kzU 2q2G9A/YFI1LL0m/gvaVbEj/wE0ybBgFkrcoEFeStkqS5HzLEFGUDFXhD80fQnVjayBDYWxh YnJvIDxrYzJoaXpAZ21haWwuY29tPsKFBBMRAgBFAhsDBgsJCAcDAgQVAggDBBYCAwECHgEC F4AFAkcbdMokGGh0dHA6Ly9rZXlzZXJ2ZXIudmVyaWRpcy5jb206MTEzNzEvAAoJEN7KcclH umuRfngAoNXU6AXqyTR8FRuoXKBGS4k7bPUEAJ912WKSkjpCt0axjrq6j22e5XgWzc7BTQRH G2k+EAgAnLXJ9hOqedgsIYM3LuomBBNN+7WTFSVaJ3Rqz8XVZtJvLL0bIRAvpVK9L9rYXlCR cPAm0YNK6H2DR7sQxWlxEH4mWB+jTCTALpcVq+Kpfbw5qDdn+9DVMS7tBOchtTlPSGgdKgn7 sTObra8cHtX/ddTB6OLzHeTXr4PZbUwVeQdIStdwMmozKBQvgjXWKi1GiuYbwYkCM/zJEUCs J36BIE4li9xohJ5O4iKC20YVckMJfZLbn1a2gVgn6Re8C5ezNewT0qM8ZDCUNENWAxsU/c9J UCFQ2QcMU+25b84D5yPxnEKna5U9Fz2JjRjWy5ZKZx2+WhZj0r2Tw6/kGb28AwADBgf/WBsn JSMHxyVfg+LKLHpdANwa9jdrKOt2WjJbWOiJ9l7SmqD0oi3c22FFxRXKsFfjCikLk9wbLZKH SqqnOePvMMHqNcqQTSv7+ARjxnBH4g6dhqg+zmebKpt8zV2awQzYSSm4YY6IqzkWmPNAN7BU zUtSAfL4UU2PljTnT9m443aVCTXMne5l90HQv/gdJ121owg5KuGE6LodTpoR4hn9nbdKWtfY pDNoykvR+GN5y335yF2Zp/j6QgdxWezjou5Y3/6PUZLEsJagWe9hAcKb1eiO2bmg+1bFYu0T g5Mvb27nqfFeHHFysC7a7sXtxp/pqNLNDcK6j/7Th6vF7/n98cJJBBgRAgAJBQJHG2k+AhsM AAoJEN7KcclHumuR9SgAnRuJWHon4GP58xbqCiFR/jSUfvRgAJ47KZ1UNoXgdftoePnbrZu6 W+poEw==
List-archive: <https://archive.midrange.com/midrange-l/>
List-help: <mailto:midrange-l-request@midrange.com?subject=help>
List-id: Midrange Systems Technical Discussion <midrange-l.midrange.com>
List-post: <mailto:midrange-l@midrange.com>
List-subscribe: <https://lists.midrange.com/mailman/listinfo/midrange-l>, <mailto:midrange-l-request@midrange.com?subject=subscribe>
List-unsubscribe: <https://lists.midrange.com/mailman/options/midrange-l>, <mailto:midrange-l-request@midrange.com?subject=unsubscribe>

On 8/28/2018 7:03 PM, Charles Wilt wrote:

If you're using Run SQL Scripts you can change to *ALLIO in the JDBC
connection config.

I can confirm that in fact, *ALLIO as an optimisation goal causes the
non-CTE to run as slowly as the CTE does. Good diagnostic, thanks.

The view (my ultimate goal) is used in stored procedures that are called
by various ODBC-centric applications as well as Good Old Fashioned
SQLRPGLE. So changing the JDBC configuration won't help out there.

I tried OPTIMIZE FOR 1 ROWS but the 7.3 TR4 optimizer doesn't use that
hint to optimise the CTE-based UNIONs. What ultimately worked for the
issue was to extract the CTE out into its own VIEW, and SELECT ... FROM
the view.

As an Amazon Associate we earn from qualifying purchases.

This mailing list archive is Copyright 1997-2025 by midrange.com and David Gibbs as a compilation work. Use of the archive is restricted to research of a business or technical nature. Any other uses are prohibited. Full details are available on our policy page. If you have questions about this, please contact [javascript protected email address].

Operating expenses for this site are earned using the Amazon Associate program and Google Adsense.