• Understanding of BTREE index and hash index


    statement1) This article collates the selfless contributions of Daniel and experts from the Internet. Please refer to the references for the specific references.2) This article is for academic exchange only, non-commercial. If a certain part violates everyone’s interests, please contact Haihan to delete it.3) The blogger is short of talent and learning. If there are […]

  • Introduction to pandas (6)


    import pandas as pd gl=pd.read_csv(‘./pandas/data/game_logs.csv’) #Memory usage of data gl.info(memory_usage=’deep’) <class ‘pandas.core.frame.DataFrame’> RangeIndex: 171907 entries, 0 to 171906 Columns: 161 entries, date to acquisition_info dtypes: float64(77), int64(6), object(78) memory usage: 859.4 MB for dtype in [‘float64′,’object’,’int64′]: selected_dtype=gl.select_dtypes(include=[dtype]) memory_usage_b=selected_dtype.memory_usage(deep=True).mean() memory_usage_mb=memory_usage_b/1024/1024 print(‘[%s] memory usage %0.2f MB’ % (dtype,memory_usage_mb)) [float64] memory usage 1.29 MB [object] memory usage 9.50 […]

  • Gaode map API: Administrative Region + range + translation + latitude and longitude + mouse style


    Get the administrative region getcity() of the current map map <span style=”background-color: #f5f5f5; color: #800000;”> *</span><span style=”background-color: #f5f5f5; color: #000000;”>{</span><span style=”background-color: #f5f5f5; color: #ff0000;”>margin</span><span style=”background-color: #f5f5f5; color: #000000;”>:</span><span style=”background-color: #f5f5f5; color: #0000ff;”>0</span><span style=”background-color: #f5f5f5; color: #000000;”>;</span><span style=”background-color: #f5f5f5; color: #ff0000;”>padding</span><span style=”background-color: #f5f5f5; color: #000000;”>:</span><span style=”background-color: #f5f5f5; color: #0000ff;”>0</span><span style=”background-color: #f5f5f5; color: #000000;”>;</span><span style=”background-color: #f5f5f5; color: […]

  • D3 learning Day1 — draw a curve


    The basic layout of D3 canvas is as follows The implementation process is as follows: First define the size of the drawing container var width = 500, height = 200, margin = { left: 50, top: 30, right: 20, bottom: 20 }, g_width = width – margin.left – margin.right, g_height = height – margin.top – […]

  • Oracle view SQL execution plan and analyze SQL performance


    How to view SQL execution plan UsePL/SQLThe specific usage is as follows: newly buildExplain the plan window, willSQLCopy in to execute, and the execution plan will be displayed. SelectSQLStatement, click menutool–Explain the planOr press the shortcut keyF5 Implementation plan result description Table scan table access by index rowid Through ROWID’s table access, I / O […]

  • Evolution of Cassandra vnodes in Cassandra 2.0-4.0


    Brief history of vnodes   Vnodes is also called virtual nodes. It’s CassandraFeatures introduced in version 1.2It has been used in production environment for nearly 8 years. From version 2.0, because num is in the default configuration_ Tokens is usually set to 256, so if you haven’t changed the default parameter, it’s very likely that […]

  • The determination of address range when two addresses of SED are regular expressions


    I was watching it yesterdaySed concise course。 When I experimented with two regular addresses, I encountered some problems, and Google couldn’t find a detailed explanation. After many experiments, it is finally clear. Let’s talk about my own understanding. The address of SED can be a line number or a regular expression. When both addresses are […]

  • Getting client IP with PHP


    REMOTE_ Addr is the IP address when your client “shakes hands” with your server. If anonymous proxy is used, remote_ Addr will display the IP of the proxy server (proxy can be used in nginx_ set_ header X-Forwarded-For $remote_ Addr; to solve the problem).HTTP_ CLIENT_ IP is the HTTP header sent by the proxy server. […]

  • Django ORM query statement


    Model.objects.all () ා gets the queryset of all objects Model.objects.filter () ා gets the queryset of the object that satisfies the condition Model.objects.exclude () ා gets the queryset of an object that does not meet the condition Model.objects.get () ා gets the queryset of a single eligible object Person.objects.all().extra(select={‘is_adult’: “age > 18”}) querySet.distinct () to […]

  • The numeric type of MySQL


    The numeric type of MySQL Integer type Integer type containsTINYINT、SMALLINT、MEDIUMINT、INT、 BIGINTEtc. Access range type Storage size Default display width (PCS) Range (signed) Range (no sign) purpose TINYINT(m) 1Byte m:4 -128 – 127 0 – 255 Small integer value SMALLINT(m) 2Byte m:6 -32768 – 32767 0 – 65535 Large integer value MEDIUMINT(m) 3Byte m:9 -8388608 – […]

  • On C language integer and floating point conversion


    This blog will elaborate and discuss the following contents: ●int The range of int varies between 16 bits or 32 bits according to different computers. Take 16 bits for example. The maximum value is 1111111111111, that is 65535. If 65536 occurs, it will overflow.      ●Signed int Taking a 16 bit system as an example, […]

  • Range partition


    Series articles: Range partition MySQL execution plan The partition method of range partition table is: each partition contains row data, and the partition expression is within the given range. The range of partition should be continuous and can not overlap, which can be defined by the values less than operator. Create common table 1 CREATE […]