Removing duplicate indices from mysql database with priority
https://stackoverflow.com/questions/12742043
-
05-07-2021 - |
italiano
english
français
española
中国
日本の
العربية
Deutsch
한국어
Português
RussianВопрос
I am making a procedure for optimizing indices of my databases and it will take me long. So I want to confirm if it is feasible to do? And not already done otherwise want to get it.
- I want to read all indices from all tables.
- I want to drop all other indices on fields which are primary key
- After doing above. The fields which are still indexed as unique. I want to drop all other indices on them
- The fields which are neither primary nor unique. I want to keep only one index on each and drop all other indices
I am curious Why MYSQL allows unique index on a primary key field? Can it make any useful difference?
Question : I need guidance/query/procedure to remove all non useful indices with the hierarchy mentioned in my above 4 points
Update 1: I will keep my work updating Here on SQLFiddle. At the moment it is just beginning. However you can see on this link that there are four fields and 8 indices. I want just 3 of them and drop all others. I need only 1st, 3rd and 4th. According to my above 4 points.
Update 2 : I got excellent answer by eggayal. First link he gave is the pure sql solution. I tried it Here at Link2. It gave me undesired output. Output of link2 can be compared by looking into Link1 here
Desired output Is
COLUMN_NAMES REDUNDANT_INDEXES 1 auth_id `auth_id_3`,`auth_id_2`,`auth_id` 2 id `id_2`,`id_3` 3 subject `subject_1`
Faults in th output of query in Link2
Row1: auth_id is not shown as redundant index because It has nothing to do (compare) with unique key auth_id_4 on the same field. But I need it because I don't need this index when same column has a unique index as well
Row2 : I will like to say all other indices redundant when there exists primary key index on some column
Row3 : All right
Решение
I have made an application in c#. It removes duplicate indices according to your priority, Hope it would help
It might need much improvements but what I know is... It does not remove only those duplicate indices which are involved in primary(composite) and foreign key at a time (which should not be usually good approach)
Here is download link for complete application with source
Following is the main file of above link
using System;
using System.Data;
using MySql.Data.MySqlClient;
using System.Collections.Generic;
namespace duplicateIndexRemover
{
public class duplicateIndexRemover
{
static List<string> toDrop;
public string main(System.Windows.Forms.DataGridView dgv, System.Windows.Forms.DataGridView dgv1, string dbName)
{
try
{
toDrop = new List<string>();
List<table> tbs = new List<table>();
DataTable dt1 = new DataTable();
string cnStr = "SERVER=localhost;DATABASE=" + dbName + ";UID=root;";
MySqlConnection conn = new MySqlConnection(cnStr);
MySqlCommand cmd = conn.CreateCommand();
cmd.CommandText = @"SELECT Table_Name,Column_Name,Index_Name,NON_UNIQUE
FROM information_schema.STATISTICS
WHERE table_schema = '" + dbName + "' order by Table_Name,Column_Name,Index_Name";
MySqlDataAdapter adp = new MySqlDataAdapter(cmd);
DataTable dt = new DataTable();
adp.Fill(dt);
dgv.DataSource = dt;
for (int i = 0; i < dt.Columns.Count - 1; i++)
dt1.Columns.Add(dt.Columns[i].ColumnName);
table tb = new table();
column cl = new column();
index dx = new index();
tb.nam = dt.Rows[0][0].ToString();
cl = addColumn(dt, tb, 0);
tbs.Add(tb);
for (int i = 1; i < dt.Rows.Count; i++)
{
if (tb.nam != dt.Rows[i][0].ToString())
{
// 1st column of (current) t_th table
tb = new table();
tb.nam = dt.Rows[i][0].ToString();
cl = addColumn(dt, tb, i);
tbs.Add(tb);
}
else
{
if (cl.nam != dt.Rows[i][1].ToString())
cl = addColumn(dt, tb, i);
else
{
// Duplicate Indices
// But this one may be primary/unique key
// Then it would not be good to make a drop statement for this index here
// It may be improvable, but i can not apply as well condition here if it is not primary key
addIndex(dt, cl, i);
}
}
}
makeDropStatements(tbs, dt1);
dgv1.DataSource = dt1;
cmd.Connection.Open();
for (int i = 0; i < toDrop.Count; i++)
{
cmd.CommandText = toDrop[i];
try
{
cmd.ExecuteScalar();
}
catch//(Exception ex)
{
//System.Windows.Forms.MessageBox.Show("Table : " + dt1.Rows[i][0] + " Column : " + dt1.Rows[i][1] + "\n\n" + ex.Message);
}
}
cmd.CommandText = @"select table_name from information_schema.STATISTICS
WHERE table_schema = '" + dbName + "' group by table_name,column_name";
DataTable dg = new DataTable();
adp.Fill(dg);
string msg = " Total Number of Indices : " + dt.Rows.Count;
msg += "\t Droppable Indices : " + toDrop.Count;
msg += "\t Total Number of Indexed Columns : " + dg.Rows.Count;
return msg;
}
catch (Exception ex)
{
System.Windows.Forms.MessageBox.Show(ex.Message);
return ex.Message;
}
}
private static column addColumn(DataTable dt, table tb, int i)
{
column cl = new column();
// 1st index of i_th column of t_th table
cl.nam = dt.Rows[i][1].ToString();
addIndex(dt, cl, i);
tb.cols.Add(cl);
return cl;
}
private static void addIndex(DataTable dt, column cl, int i)
{
index dx = new index();
dx.nam = dt.Rows[i][2].ToString();
dx.non_unique = Convert.ToBoolean(dt.Rows[i][3]);
cl.indices.Add(dx);
}
private static void makeDropStatements(List<table> tbs, DataTable dt1)
{
bool chekd;
List<index> temp;
for (int t = 0; t < tbs.Count; t++)
{
for (int i = 0; i < tbs[t].cols.Count; i++)
{
temp = tbs[t].cols[i].indices;
if (temp.Count > 1)
{
chekd = false;
for (int j = 0; j < temp.Count; j++)
{
if (temp[j].nam == "PRIMARY")
{
getToDropIndices(tbs[t].nam, tbs[t].cols[i].nam, temp, j, dt1);
chekd = true;
break;
}
}
if (!chekd)
{
for (int j = 0; j < temp.Count; j++)
{
if (!temp[j].non_unique)
{
getToDropIndices(tbs[t].nam, tbs[t].cols[i].nam, temp, j, dt1);
chekd = true;
break;
}
}
}
if (!chekd)
{
getToDropIndices(tbs[t].nam, tbs[t].cols[i].nam, temp, 0, dt1);
chekd = true;
break;
}
}
}
}
}
private static void getToDropIndices(string tbl, string col, List<index> sublist, int nt, DataTable dt1)
{
for (int j = 0; j < nt; j++)
{
toDrop.Add("alter table `" + tbl + "` drop index " + sublist[j].nam);
dt1.Rows.Add(dt1.NewRow());
int r = dt1.Rows.Count - 1;
dt1.Rows[r][0] = tbl;
dt1.Rows[r][1] = col;
dt1.Rows[r][2] = sublist[j].nam;
}
for (int j = nt + 1; j < sublist.Count; j++)
{
toDrop.Add("alter table `" + tbl + "` drop index " + sublist[j].nam);
dt1.Rows.Add(dt1.NewRow());
int r = dt1.Rows.Count - 1;
dt1.Rows[r][0] = tbl;
dt1.Rows[r][1] = col;
dt1.Rows[r][2] = sublist[j].nam;
}
}
}
public class table
{
public List<column> cols =new List<column>();
public string nam = "";
}
public class column
{
public List<index> indices = new List<index>();
public string nam = "";
}
public class index
{
public string nam = "";
public bool non_unique;
}
}
You may ignore/remove gridviews they are just for showing your indices. You just need to call main function
Другие советы
Roland Bouman wrote a blog article on this very subject, showing a pure SQL solution.
A quick search on Google also churned up:
DuplicateIndexFinder.java;- A similar tool written in Perl that was part of maatkit, now Percona Toolkit; and
mysqlindexanalyzer.
Based on what I see in the link there do seem to be a number of extraneous indexes like these:
KEY `auth_id_2` (`auth_id`),
KEY `auth_id_4` (`auth_id`),
KEY `auth_id_5` (`auth_id`),
KEY `auth_id_6` (`auth_id`)
I thought maybe they were built in different ways. For instance one could be a BTREE and another a HASH, which could potentially serve some purpose. But they're all the same according to SHOW. Removing the extra identical ones should not be an issue.
There is a purpose to having, for instance, all three of these though:
KEY `articleid` (`artid`),
KEY `artSub` (`artSub`),
KEY `comments_ibfk_3` (`artSub`,`artid`)
Building the index on two columns is not necessarily the same as building two separate indexes on one.
