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Fri Jul 21 17:24:58 HKT 2017
From /weblog/database/performance
Note of this book - http://www.ocelot.ca/tuning.htm 1) Order of "and" and "or" is matter, if no cost-base optimizer where column1 = 'a' and column2 = 'b' -> where column2 = 'b' and column1 = 'a' if column2 'b' is less likely 2) <> is more expensive than = 3) Can force to use index if SELECT * FROM table WHERE indexed_column > 0 4) UPPER(column) might lose information, use LOWER is better 5) WHERE column = 'WORD' or column = 'word' is always faster than WHERE LOWER(column) = 'word' , even faster version is test if database if case-insensitive: WHERE column = 'WORD' or ('WORD' <> 'word' AND column = 'word') 6) 32bit integer is the fastest datatype for 32bit OS 7) column in (?, ?) is faster than column =? or column = ? for some database, and don't slow in any database 8) For aggregate functions, prevent using having, try to use fewer columns in group by and use subquery if possible 9) In fact, count(1) is not faster than count(*) 10) CAST before aggregate function: SELECT CAST(SUM(column) AS INT) -> SELECT SUM(CAST(column as INT)) 11) Use constant as much as possible, e.g.: select * from t1, t2 where t1.c1 = t2.c1 and t1.c1 = 1 -> select * from t1, t2 where t1.c1=1 andn t2.c1=1 12) Information of Join vs Subqueries 13) Information of optimum column type (VARCHAR, TIMESTAMP, WORD size INT and CHAR(1) usually better), shift effect for page 14) prevent NULL for porting issue 15) Low level table physical information Some related links - http://www.techartifact.com[..]9/12/sql-optimization-tipsquestions.html 16) Prevent database level transaction, prevent joining, prevent locking ( like auto increment key ), pretty good suggestion - http://www.aviransplace.com/2015/08/12/mysql-is-a-great-nosql/ Few good tips, like avoid cursors - http://www.javaworld.com[..]ent/21-rules-for-faster-sql-queries.html
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Thu Jul 20 00:11:49 HKT 2017
From /weblog/learning
In other words, both groups were stressed, but one group channeled the stress as a performance challenge; the other group as a performance threat. It wasn't the stress of a difficult test that caused distress--everyone felt that. It was how subjects interpreted their stress. - http://traderfeed.blogspot.com.au[..]mbracing-stress-minimizing-distress.html http://nautil.us/blog/do-you-actually-need-more-stress Calming when conflict - https://hbr.org/2015/12/calming-your-brain-during-conflict https://aeon.co[..]ks-in-the-human-body-to-make-or-break-us
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Thu Jul 13 15:54:32 HKT 2017
From /weblog/misc
Short tips of regex - http://immike.net[..]know-to-become-a-regular-expression-pro/ Let regex more readable - http://martinfowler.com/bliki/ComposedRegex.html Useful Regular regression Match username - /^[a-zA-Z0-9_]{3,16}$/ Matching an XHTML/XML tag - { ]*>(.*?)}
Matching an XHTML/XML tag with a certain attribute value (e.g. class or tag) - {]*attribute\\s*=\\s*(["'])value\\\\1[^>]*>(.*?)}
Matching a URL - (a very long one... refer to article...)
http://immike.net[..]ssions-every-web-programmer-should-know/
The danger of bad regex - http://andreas.haufler.info[..]o-kill-java-with-regular-expression.html http://www.regular-expressions.info/catastrophic.html http://vladmihalcea.com/2014/02/24/the-regex-that-broke-a-server/
You have a string “BEFOREAFTER”. If this string has a ‘x’ in it, you want to capture everything before the ‘x’, else you want to capture the whole string. So,
”BEFOREAFTER” gives “BEFOREAFTER”
”BEFORExAFTER” gives “BEFORE”
http://octodecillion.com[..]apture-with-optional-delimeter/#solution
http://www.infoq.com[..]/regular-expressions-introduction-part01
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Wed Jul 12 14:46:08 HKT 2017
From /weblog/photographic
星軌拍攝技巧 數問 - 1).數碼機因hot pixel而唔適合曝得耐...最好分開影影夠幾個鐘...咁每張間隔之間都要俾CMOS斗下氣？ 有師兄 教過 分十幾張 每張 10-20min 再合成 好過 一野 暴 幾粒鐘, (菲林 令計) 2).數碼機有D人話用ISO 100、有人話用ISO 400-800好...如果用合成方法...其實係咪都係就番光害而定...定係關雜訊事？ 睇天氣 , 小弟 用 o個次 用 iso 100 5).北極星仰角澳門係23度，咁香港一樣？？ 4季 都唔同 位置, 用星座 搵 會準確 d, e+ 係 冬季, 北極星 位置 係 獵戶座 (lei 個最易 認, 唔會 搵唔倒 ... ) 頭頂 (腰帶 致 頭頂 距離 再過 5倍左右) 附圖 係 舊年 去雲南 香格里拉 時影, 本泥想 長暴, 不過 o個晚 太涷 個人 頂唔順 要收皮 反酒店 http://www.dchome.net/viewthread.php?tid=798154 With a lot of information, 香港的星空 — 觀測及拍攝資訊 - http://www.dcfever.com/column/read.php?id=1829 Herman's articles at dcfever - http://www.dcfever.com/column/info.php?id=185 500px tutorial - http://500px.com/blog/738/tutorial-photograph-the-night-sky About Comet - http://www.dcfever.com/column/read.php?id=2193 Atmospheric optical phenomena 大氣光學現象 - http://matthew-chin.blogspot.hk[..]16/06/atmospheric-optical-phenomena.html ===== 這張是11月15日凌晨拍攝的M42獵戶座星雲, 大埔的光害較嚴重, 所以要加上IDAS V4濾鏡作長時間曝光, 分三段不同時間曝光及作Layer Masking 處理, 把動態範圍拉闊. 在月光的影下算是滿意, 希望之後可以分數晚作10小時以上的曝光並加長每一張frame 的曝光時間 (現在是5分鐘一張), 使到暗位的表現進一步改善. Place: Tai Po Date: 14 Nov, 2013 (UT) Camera: Canon 20Da Lens: Canon EF-600 F4L Mount: Vixen Sphinx with Star Book Filter: IDAS V4 Exposure: 10 sec x 10, 30 sec x 10, 300sec x 26 ISO: 800 Guiding: Borg 60mm telescope, AIS120MM, PHD guiding. Image calibration: Dark x 20 (average) for each exposure, Bias x 16 (Median), Dark subtracted Flat field x 20 (Median) Processing: DSS, PS: layer Mask, Cropped, curve, colour adjusted. http://forum.hkas.org.hk/viewthread.php?tid=8009 ===== http://list25.com[..]resemble-things-found-on-earth/?view=all how-to-find-the-milky-way - http://goldpaintphotography.com[..]om/2015/07/24/how-to-find-the-milky-way/ how-to-capture-sharp-star-photographs - http://www.mikkolagerstedt.com[..]10/how-to-capture-sharp-star-photographs 銀河 - 觀測和拍攝 - http://matthew-chin.blogspot.hk/2016/06/blog-post.html 簡易四步驟處理高清銀河 - http://www.dcfever.com/column/read.php?id=3278 TimeLapse-AfterEffects特效『星流跡影片』-進階 - http://www.dcfever.com/column/read.php?id=3935 500 rule: 11mm: 45.5 seconds 12mm: 41.7 seconds 14mm: 35.7 seconds 16mm: 31.3 seconds 18mm: 27.8 seconds 20mm: 25 seconds 24mm: 20.8 seconds 28mm: 17.9 seconds 35mm: 14.3 seconds 50mm: 10 seconds 85mm: 5.9 seconds http://www.price.com.hk/news.php?sec_id=12&id=7216 How to find constellations: a starter’s guide - http://www.zmescience.com[..]eature-post/starter-guide-constellations 想拍漂亮的散景靜物嗎？6步驟DIY一個超絢麗散景牆, with 鋁箔或銀色包裝紙 - http://digiphoto.techbang.com[..]steps-to-a-super-gorgeous-diy-bokeh-wall http://www.deepskycolors.com[..]ilky-Way-Photo-Concepts-You-May-Wan.html
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