Let's understand what are the available options to get an accurate number or an estimation of rows in a MySQL table. The option to get an accurate count of rows in a table is to perform: SELECT COUNT(*) FROM [table]; In MyISAM this operation, when no WHERE clause is provided, is very quick, as the storage engine knows at any time how many rows are in the table. When dealing with InnoDB storage engine, instead, there is no counter available. This is due to the transactional nature of this … [Read more...] about Counting Rows Of A Table In MySQL Server
How to Rebuild GRUB on MSDOS Partition Type in CentOS/RHEL/OEL 7
Question: How to Rebuild Grub on Linux servers with MSDOS Partition type. (proc) (hd0) (hd0,msdos5) (hd0,msdos3) (hd0,msdos2) (hd0,msdos1) 1. Execute the following commands in Grub prompt to set the root device and to load the boot image and initialize boot loader. > set root=(hd0,msdos1) > linux16 /vmlinuz-3.10.0-327.el7.x86_64 root=/dev/sda5 > initrd16 /initramfs-3.10.0-327.el7.x86_64.img Then boot the server. 2. Once the server boots up, rebuild the Grub config file. You can edit … [Read more...] about How to Rebuild GRUB on MSDOS Partition Type in CentOS/RHEL/OEL 7
How to Disable AUTOEXTEND Mode on a datafile in Oracle Database
Question: How do you take a datafile out of autoextend mode? Oracle datafiles were given the ability to extend automatically if needed from a long time. If the given datafile is unable to allocate the space needed, it can increase the size of the datafile to make space for objects to grow. To determine if the datafile has autoextend capabilities, query the dba_data_files table. For example: SQL> select file_name, autoextensible from dba_data_files; FILE_NAME … [Read more...] about How to Disable AUTOEXTEND Mode on a datafile in Oracle Database
Oracle – How To Check if Autoextensible Datafiles Set To Maxsize Unlimited
Question: How to check whether the datafiles are set to AUTOEXTEND and UNLIMITED? We can query the DBA_DATA_FILES view to check whether the data file is in AUTOEXTEND mode. SQL> select tablespace_name, file_name, autoextensible from dba_data_files; To confirm whether the maxsize is set to UNLIMITED we have to check for the maximum possible size, as there is no concept of an 'UNLIMITED' file size. Oracle limits the number of blocks in a datafile to approximately 4 million blocks (unless … [Read more...] about Oracle – How To Check if Autoextensible Datafiles Set To Maxsize Unlimited
Failed to Download Metadata for Repo ‘repo_name’
The Problem All the dnf commands fail with the following error: # dnf repolist Oracle Linux 8 BaseOS Latest (x86_64) 0.0 B/s | 0 B 00:00 Failed to download metadata for repo 'ol8_baseos_latest' Error: Failed to download metadata for repo 'ol8_baseos_latest dnf was not able to refresh the cache as it could not reach the yum server itself, Hence pointing to cache being expired. # yum clean metadata Cache was expired … [Read more...] about Failed to Download Metadata for Repo ‘repo_name’
How to configure Linux Resource Groups (cgroups) for MySQL
The following provides the procedure for configuring and using resource groups under Linux: 1. To use cgroups, you must install the "libcgroup" package on your system. # yum install libcgroup 2. Create a config file for cgroups (/etc/cgconfig.conf) and add below configuration. # vi /etc/cgconfig.conf mount { cpu = /cgroup/cpumem; cpuset = /cgroup/cpumem; memory = /cgroup/cpumem; } # High priority group group mysqldb { cpu { # Allocate the relative share of CPU resources … [Read more...] about How to configure Linux Resource Groups (cgroups) for MySQL
Oracle SQL Script to Detect Tablespace Fragmentation
The following is a script that will determine how many extents of contiguous free space you have in Oracle as well as the total amount of free space you have in each tablespace. From these results, you can detect how fragmented your tablespace is. The ideal situation is to have one large free extent in your tablespace. The more extents of free space there are in the tablespace, the more likely you will run into fragmentation problems. The size of the free extents is also very important. … [Read more...] about Oracle SQL Script to Detect Tablespace Fragmentation
MySQL Table Maintenance – InnoDB, MyISAM, MEMORY, ARCHIVE
InnoDB Table Maintenance If a table check indicates problems, restore the table to a consistent state by dumping it with mysqldump, dropping it, and re-creating it from the dump file. In the event of a crash of the MySQL server or the host on which it runs, some InnoDB tables might be in an inconsistent state. InnoDB performs auto-recovery as part of its startup sequence. Use CHECK TABLE or a client program to find inconsistencies, incompatibilities, and other problems. Restore a table by … [Read more...] about MySQL Table Maintenance – InnoDB, MyISAM, MEMORY, ARCHIVE
Understanding mysqlcheck and myisamchk utilities
mysqlcheck Client Program In some cases, mysqlcheck is more convenient than issuing SQL statements directly. For example, if you provide it with a database name as its argument, mysqlcheck determines what tables the database contains and issues statements to process them all. You do not need to provide explicit table names as arguments. Also, because mysqlcheck is a command-line program, you can easily use it in operating system jobs that perform scheduled maintenance. mysqlcheck is a … [Read more...] about Understanding mysqlcheck and myisamchk utilities
CentOS/RHEL – How to Remove stale ISCSI Target Node Information from ISCSI Initiator Server
The Problem Stale ISCSI target connections which are still present on Initiator node can lead to various issues like: 1. hung iscsid service which can lead to global outage. 2. flood of messages error like: messages:Jun 3 13:58:00 server1 iscsid: iscsid: Connection5:0 to [target: iqn-name, portal: ip-here,3260] through [iface: default] is shutdown. messages:Jun 3 13:58:00 server1 iscsiadm: iscsiadm: Could not login to [iface: default, target: iqn-name, portal: ip-here,3260]. messages:Jun … [Read more...] about CentOS/RHEL – How to Remove stale ISCSI Target Node Information from ISCSI Initiator Server