versioned_docs/version-2.x/deployment/single-node.md - cloudberry-site - Git at Google

 ---
 title: (Optional) Deploy with a Single Computing Node
 ---

 # Deploy Apache Cloudberry with a Single Computing Node

 Apache Cloudberry is not fully compatible with PostgreSQL, and some features and syntax are Apache Cloudberry-specific. If your business already relies on Apache Cloudberry and you want to use the Apache Cloudberry-specific syntax and features on a single node to avoid compatibility issues with PostgreSQL, you can consider deploying Apache Cloudberry free of segments.

 Apache Cloudberry provides the single-computing-node deployment mode. This mode runs under the `utility` gp_role, with only one coordinator (QD) node and one coordinator standby node, without a segment node or data distribution. You can directly connect to the coordinator and run queries as if you were connecting to a regular multi-node cluster. Note that some SQL statements are not effective in this mode because data distribution does not exist, and some SQL statements are not supported. See [user behavior changes](#user-behavior-changes) for details.

 ## How to deploy

 ### Step 1. Prepare to deploy

 Log into each host as the root user, and modify the settings of each node server in the order of the following sections.

 #### Add `gpadmin` admin user

 Follow the example below to create a user group and username `gpadmin`. Set the user group and username identifier to `520`. Create and specify the `gpadmin` home directory `/home/gpadmin`.

 ```bash
 groupadd -g 520 gpadmin  # Adds user group gpadmin.
 useradd -g 520 -u 520 -m -d /home/gpadmin/ -s /bin/bash gpadmin  # Adds username gpadmin and creates the home directory of gpadmin.
 passwd gpadmin  # Sets a password for gpadmin; after executing, follow the prompts to input the password.
 ```

 #### Disable SELinux and firewall software

 Run `systemctl status firewalld` to view the firewall status. If the firewall is on, you need to turn it off by setting the `SELINUX` parameter to `disabled` in the `/etc/selinux/config` file.

 ```bash
 SELINUX=disabled
 ```

 You can also disable the firewall using the following commands:

 ```bash
 systemctl stop firewalld.service
 systemctl disable firewalld.service
 ```

 #### Set system parameters

 Add relevant system parameters in the `/etc/sysctl.conf` configuration file, and run the `sysctl -p` command to make the configuration file effective.

 When setting the configuration parameters, you can take the following example as a reference and set them according to your needs. Details of some of these parameters and recommended settings are provided below.

 ```bash
 kernel.shmall = _PHYS_PAGES / 2
 kernel.shmall = 197951838
 kernel.shmmax = kernel.shmall * PAGE_SIZE
 kernel.shmmax = 810810728448
 kernel.shmmni = 4096
 vm.overcommit_memory = 2
 vm.overcommit_ratio = 95
 net.ipv4.ip_local_port_range = 10000 65535
 kernel.sem = 250 2048000 200 8192
 kernel.sysrq = 1
 kernel.core_uses_pid = 1
 kernel.msgmnb = 65536
 kernel.msgmax = 65536
 kernel.msgmni = 2048
 net.ipv4.tcp_syncookies = 1
 net.ipv4.conf.default.accept_source_route = 0
 net.ipv4.tcp_max_syn_backlog = 4096
 net.ipv4.conf.all.arp_filter = 1
 net.ipv4.ipfrag_high_thresh = 41943040
 net.ipv4.ipfrag_low_thresh = 31457280
 net.ipv4.ipfrag_time = 60
 net.core.netdev_max_backlog = 10000
 net.core.rmem_max = 2097152
 net.core.wmem_max = 2097152
 vm.swappiness = 10
 vm.zone_reclaim_mode = 0
 vm.dirty_expire_centisecs = 500
 vm.dirty_writeback_centisecs = 100
 vm.dirty_background_ratio = 0
 vm.dirty_ratio = 0
 vm.dirty_background_bytes = 1610612736
 vm.dirty_bytes = 4294967296
 ```

 ##### Shared memory settings

 In the `/etc/sysctl.conf` configuration file, `kernel.shmall` represents the total amount of available shared memory, in pages. `kernel.shmmax` represents the maximum size of a single shared memory segment, in bytes.

 You can define these 2 values using the operating system's `_PHYS_PAGES` and `PAGE_SIZE` parameters:

 ```
 kernel.shmall = ( _PHYS_PAGES / 2)
 kernel.shmmax = ( _PHYS_PAGES / 2) * PAGE_SIZE
 ```

 To get the values of these 2 operating system parameters, you can use `getconf`, for example:

 ```bash
 $echo $(expr $(getconf _PHYS_PAGES)/2)
 $echo $(expr $(getconf _PHYS_PAGES)/2 \*$(getconf PAGE_SIZE))
 ```

 - `vm.overcommit_memory` indicates the overcommit handling modes for memory. Available options are:

     - `0`: Heuristic overcommit handling
     - `1`: Always overcommit
     - `2`: Don't overcommit

     Set the value of this parameter to `2` to refuse overcommit.

 - `vm.overcommit_ratio` is a kernel parameter and is the percentage of RAM occupied by the application process. The default value on CentOS is `50`. `vm.overcommit_ratio` is calculated as follows:

     ```
     vm.overcommit_ratio = (RAM - 0.026 * gp_vmem) / RAM
     ```

 - The calculation method of `gp_vmem` is as follows:

     ```
     # If the system memory is less than 256 GB, use the following formula to calculate:
     gp_vmem = ((SWAP + RAM) – (7.5GB + 0.05 * RAM)) / 1.7

     # If the system memory is greater than or equal to 256 GB, use the following formula to calculate:
     gp_vmem = ((SWAP + RAM) – (7.5GB + 0.05 * RAM)) / 1.17

     # In the above formulas, SWAP is the swap space on the host, in GB.
     # RAM is the size of the memory installed on the host, in GB.
     ```

 ##### IP segmentation settings

 When the Apache Cloudberry uses the UDP protocol for internal connection, the network card controls the fragmentation and reassembly of IP packets. If the size of a UDP message is larger than the maximum size of network transmission unit (MTU), the IP layer fragments the message.

 - `net.ipv4.ipfrag_high_thresh`: When the total size of IP fragments exceeds this threshold, the kernel will attempt to reorganize IP fragments. If the fragments exceed this threshold but all fragments have not arrived within the specified time, the kernel will not reorganize the fragments. This threshold is typically used to control whether larger shards are reorganized. The default value is `4194304` bytes (4 MB).
 - `net.ipv4.ipfrag_low_thresh`: Indicates that when the total size of IP fragments is below this threshold, the kernel will wait as long as possible for more fragments to arrive, to allow for larger reorganizations. This threshold is used to minimize unfinished reorganization operations and improve system performance. The default value is `3145728` bytes (3 MB).
 - `net.ipv4.ipfrag_time` is a kernel parameter that controls the IP fragment reassembly timeout. The default value is `30`.

 It is recommended to set the above parameters to the following values:

 ```
 net.ipv4.ipfrag_high_thresh = 41943040
 net.ipv4.ipfrag_low_thresh = 31457280
 net.ipv4.ipfrag_time = 60
 ```

 ##### System memory

 - If the server memory exceeds 64 GB, the following parameters are recommended in the `/etc/sysctl.conf ` configuration file:

     ```
     vm.dirty_background_ratio = 0
     vm.dirty_ratio = 0
     vm.dirty_background_bytes = 1610612736 # 1.5GB
     vm.dirty_bytes = 4294967296 # 4GB
     ```

 - If the server memory is less than 64 GB, you do not need to set `vm.dirty_background_bytes ` or `vm.dirty_bytes`. It is recommended to set the following parameters in the `/etc/sysctl.conf ` configuration file:

     ```
     vm.dirty_background_ratio = 3
     vm.dirty_ratio = 10
     ```

 - To deal with emergency situations when the system is under memory pressure, it is recommended to add the `vm.min_free_kbytes` parameter to the `/etc/sysctl.conf` configuration file to control the amount of available memory reserved by the system. It is recommended to set `vm.min_free_kbytes` to 3% of the system's physical memory, with the following command:

     ```bash
     awk 'BEGIN {OFMT = "%.0f";} /MemTotal/ {print "vm.min_free_kbytes =", $2 * .03;}' /proc/meminfo  /etc/sysctl.conf
     ```

 - The setting of `vm.min_free_kbytes` is not recommended to exceed 5% of the system's physical memory.

 ##### Resource limit

 Edit the `/etc/security/limits.conf` file and add the following content, which will limit the amount of hardware and software resources.

 ```
 *soft nofile 524288
 *hard nofile 524288
 *soft nproc 131072
 *hard nproc 131072
 ```

 ##### CORE DUMP

 1. Add the following parameter to the `/etc/sysctl.conf` configuration file:

     ```
     kernel.core_pattern=/var/core/core.%h.%t
     ```

 2. Run the following command to make the configuration effective:

     ```bash
     sysctl -p
     ```

 3. Add the following parameter to `/etc/security/limits.conf`:

     ```
     * soft core unlimited
     ```

 ##### Set mount options for the XFS file system

 XFS is the file system for the data directory of Apache Cloudberry. XFS has the following mount options:

 ```
 rw,nodev,noatime,inode64
 ```

 You can set up XFS file mounting in the `/etc/fstab` file. See the following commands. You need to choose the file path according to the actual situation:

 ```bash
 mkdir -p /data0/
 mkfs.xfs -f /dev/vdc
 echo "/dev/vdc /data0 xfs rw,nodev,noatime,inode64 0 0"  /etc/fstab
 mount /data0
 chown -R gpadmin:gpadmin /data0/
 ```

 :::note
 The `nobarrier` option is not supported on RHEL 8/9 or Ubuntu systems. Use only the options `rw,nodev,noatime,inode64`.
 :::

 Run the following command to check whether the mounting is successful:

 ```bash
 df -h
 ```

 ##### Blockdev value

 The blockdev value for each disk file should be `16384`. To verify the blockdev value of a disk device, use the following command:

 ```bash
 sudo/sbin/blockdev --getra<devname>
 ```

 For example, to verify the blockdev value of the example server disk:

 ```bash
 sudo/sbin/blockdev --getra /dev/vdc
 ```

 To modify the blockdev value of a device file, use the following command:

 ```bash
 sudo/sbin/blockdev --setra<bytes> <devname>
 ```

 For example, to modify the file blockdev value of the hard disk of the example server:

 ```bash
 sudo/sbin/blockdev --setra16384/dev/vdc
 ```

 ##### I/O scheduling policy settings for disks

 The disk type, operating system, and scheduling policies of Apache Cloudberry are as follows:

 <table>
 <thead>
   <tr>
     <th>Storage device type</th>
     <th>OS</th>
     <th>Recommended scheduling policy</th>
   </tr>
 </thead>
 <tbody>
   <tr>
     <td rowspan="3">NVMe</td>
   </tr>
   <tr>
     <td>RHEL 8</td>
     <td>none</td>
   </tr>
   <tr>
     <td>Ubuntu</td>
     <td>none</td>
   </tr>
   <tr>
     <td rowspan="3">SSD</td>
   </tr>
   <tr>
     <td>RHEL 8</td>
     <td>none</td>
   </tr>
   <tr>
     <td>Ubuntu</td>
     <td>none</td>
   </tr>
   <tr>
     <td rowspan="3">Other</td>
   </tr>
   <tr>
     <td>RHEL 8</td>
     <td>mq-deadline</td>
   </tr>
   <tr>
     <td>Ubuntu</td>
     <td>mq-deadline</td>
   </tr>
 </tbody>
 </table>

 Refer to the following command to modify the scheduling policy. Note that this command is only a temporary modification, and the modification becomes invalid after the server is restarted.

 ```bash
 echo schedulername>/sys/block/<devname>/queue/scheduler
 ```

 For example, temporarily modify the disk I/O scheduling policy of the example server:

 ```bash
 echo deadline>/sys/block/vdc/queue/scheduler
 ```

 To permanently modify the scheduling policy, use the system utility `grubby`. After using `grubby`, the modification takes effect immediately after you restart the server. The sample command is as follows:

 ```bash
 grubby --update-kernel=ALL --args="elevator=deadline"
 ```

 To view the kernel parameter settings, use the following command:

 ```bash
 grubby --info=ALL
 ```

 ##### Disable Transparent Huge Pages (THP)

 You need to disable Transparent Huge Pages (THP), because it reduces database performance. The command is as follows:

 ```bash
 grubby --update-kernel=ALL --args="transparent_hugepage=never"
 ```

 Check the status of THP:

 ```bash
 cat /sys/kernel/mm/*transparent_hugepage/enabled
 ```

 ##### Disable IPC object deletion

 Disable IPC object deletion by setting the value of `RemoveIPC` to `no`. You can set this parameter in the `/etc/systemd/logind.conf` file of Apache Cloudberry.

 ```
 RemoveIPC=no
 ```

 After disabling it, run the following command to restart the server to make the disabling setting effective:

 ```bash
 service systemd-logind restart
 ```

 ##### SSH connection threshold

 To set the SSH connection threshold, you need to modify the `MaxStartups` and `MaxSessions` parameters in the `/etc/ssh/sshd_config` configuration file. Both of the following writing methods are acceptable.

 ```
 MaxStartups 200
 MaxSessions 200
 ```

 ```
 MaxStartups 10:30:200
 MaxSessions 200
 ```

 Run the following command to restart the server to make the setting take effect:

 ```bash
 service sshd restart
 ```

 ##### Clock synchronization

 Apache Cloudberry requires the clock synchronization to be configured for all hosts, and the clock synchronization service should be started when the host starts. You can choose one of the following synchronization methods:

 - Use the coordinator node's time as the source, and other hosts synchronize the clock of the coordinator node host.
 - Synchronize clocks using an external clock source.

 The example in this document uses an external clock source for synchronization, that is, adding the following configuration to the `/etc/chrony.conf` configuration file:

 ```
 # Use public servers from the pool.ntp.org project.
 # Please consider joining the pool (http://www.pool.ntp.org/join.html).
 server 0.centos.pool.ntp.org iburst
 ```

 After setting, you can run the following command to check the clock synchronization status:

 ```bash
 systemctl status chronyd
 ```

 ### Step 2. Install Apache Cloudberry

 :::info
 Starting from Apache Cloudberry 2.1, RPM and DEB packages are officially provided. RPM packages support Rocky Linux 8/9, RHEL 8/9, and compatible distributions. DEB packages support Ubuntu 22.04.
 :::

 1. Download the package to the home directory of `gpadmin`.

 2. Install the package in the `/home/gpadmin` directory.

     When running the following command, you need to replace `<package path>` with the actual package path, as the `root` user. During the installation, the directory `/usr/local/cloudberry-db/` is automatically created.

     ```bash
     cd /home/gpadmin

    # For RPM (Rocky Linux, RHEL, etc.)
     dnf install <RPM package path>
     # Or for older systems: yum install <RPM package path>

     # For DEB (Ubuntu)
     apt install <DEB package path>
     # Or alternatively: dpkg -i <DEB package path> && apt-get install -f
     ```

 3. Grant the `gpadmin` user the permission to access the `/usr/local/cloudberry-db/` directory.

     ```bash
     chown -R gpadmin:gpadmin /usr/local/cloudberry*
     ```

 4. Configure local SSH connection for the node. As the `gpadmin` user, perform the following operations:

     ```bash
     ssh-keygen
     ssh-copy-id localhost
     ssh `hostname` # Makes sure that the local SSH connection works well.
     ```

 ### Step 3. Deploy Apache Cloudberry with a single computing node

 Use the scripting tool [`gpdemo`](/docs/sys-utilities/gpdemo.md) to quickly deploy Apache Cloudberry. `gpdemo` is included in the RPM package and will be installed in the `GPHOME/bin` directory along with the configuration scripts (gpinitsystem, gpstart, and gpstop). `gpdemo` supports quickly deploying Apache Cloudberry with a single computing node.

 In the above [setting mount options for the XFS file system](#set-mount-options-for-the-xfs-file-system), the XFS  file system's data directory is mounted on `/data0`. The following commands deploy a single-computing-node cluster in this data directory:

 ```bash
 cd /data0
 NUM_PRIMARY_MIRROR_PAIRS=0 gpdemo  # Uses gpdemo
 ```

 When `gpdemo` is running, a warning will be output `[WARNING]: -SinglenodeMode has been enabled, no segment will be created.`, which indicates that Apache Cloudberry is currently being deployed in the single-computing-node mode.

 ## Common issues

 ### How to check the deployment mode of a cluster

 Perform the following steps to confirm the deployment mode of the current Apache Cloudberry cluster:

 1. Connect to the coordinator node.
 2. Execute `SHOW gp_role;` to view the operating mode of the cluster.

     - If `utility` is returned, it indicates that the cluster is in utility mode (maintenance mode), where only the coordinator node is available.

         Continue to run the `SHOW gp_internal_is_singlenode;` command to see whether the cluster is in the single-computing-node mode.

         - If `on` is returned, the current cluster is in the single-computing-node mode.
         - If `off` is returned, the current cluster is in utility maintenance mode.

     - If `dispatch` is returned, it means that the current cluster is a regular cluster containing segment nodes. You can further check the segment count, status, port, data directory, and other information of the cluster by running `SELECT * FROM n;`.

 ### Where is the data directory

 `gpdemo` automatically creates a data directory in the current path (`$PWD`). For the single-computing-node deployment:

 - The default directory of the coordinator is `./datadirs/singlenodedir`.
 - The default directory of the coordinator standby node is `./datadirs/standby`.

 ## How it works

 When you are deploying Apache Cloudberry in the single-computing-node mode, the deployment script `gpdemo` writes `gp_internal_is_singlenode = true` to the configuration file `postgresql.conf` and starts a coordinator and a coordinator standby node with the `gp_role = utility` parameter setting. All data is written locally without a segment or data distribution.

 ## User-behavior changes

 In the single-computing-node mode, the product behavior of Apache Cloudberry has the following changes. You should pay attention to these changes before performing related operations:

 - When you execute `CREATE TABLE` to create a table, the `DISTRIBUTED BY` clause no longer takes effect. A warning is output: `WARNING: DISTRIBUTED BY clause has no effect in singlenode mode`.
 - The `SCATTER BY` clause of the `SELECT` statement is no longer effective. A warning is output: `WARNING: SCATTER BY clause has no effect in singlenode mode`.
 - Other statements that are not supported (for example, `ALTER TABLE SET DISTRIBUTED BY`) are declined with an error.
 - The lock level of `UPDATE` and  `DELETE` statements will be reduced from  `ExclusiveLock` to  `RowExclusiveLock` to provide better concurrency performance, because there is only a single node without global transactions or global deadlocks. This behavior is consistent with PostgreSQL.
	---
	title: (Optional) Deploy with a Single Computing Node
	---

	# Deploy Apache Cloudberry with a Single Computing Node

	Apache Cloudberry is not fully compatible with PostgreSQL, and some features and syntax are Apache Cloudberry-specific. If your business already relies on Apache Cloudberry and you want to use the Apache Cloudberry-specific syntax and features on a single node to avoid compatibility issues with PostgreSQL, you can consider deploying Apache Cloudberry free of segments.

	Apache Cloudberry provides the single-computing-node deployment mode. This mode runs under the `utility` gp_role, with only one coordinator (QD) node and one coordinator standby node, without a segment node or data distribution. You can directly connect to the coordinator and run queries as if you were connecting to a regular multi-node cluster. Note that some SQL statements are not effective in this mode because data distribution does not exist, and some SQL statements are not supported. See [user behavior changes](#user-behavior-changes) for details.

	## How to deploy

	### Step 1. Prepare to deploy

	Log into each host as the root user, and modify the settings of each node server in the order of the following sections.

	#### Add `gpadmin` admin user

	Follow the example below to create a user group and username `gpadmin`. Set the user group and username identifier to `520`. Create and specify the `gpadmin` home directory `/home/gpadmin`.

	```bash
	groupadd -g 520 gpadmin # Adds user group gpadmin.
	useradd -g 520 -u 520 -m -d /home/gpadmin/ -s /bin/bash gpadmin # Adds username gpadmin and creates the home directory of gpadmin.
	passwd gpadmin # Sets a password for gpadmin; after executing, follow the prompts to input the password.
	```

	#### Disable SELinux and firewall software

	Run `systemctl status firewalld` to view the firewall status. If the firewall is on, you need to turn it off by setting the `SELINUX` parameter to `disabled` in the `/etc/selinux/config` file.

	```bash
	SELINUX=disabled
	```

	You can also disable the firewall using the following commands:

	```bash
	systemctl stop firewalld.service
	systemctl disable firewalld.service
	```

	#### Set system parameters

	Add relevant system parameters in the `/etc/sysctl.conf` configuration file, and run the `sysctl -p` command to make the configuration file effective.

	When setting the configuration parameters, you can take the following example as a reference and set them according to your needs. Details of some of these parameters and recommended settings are provided below.

	```bash
	kernel.shmall = _PHYS_PAGES / 2
	kernel.shmall = 197951838
	kernel.shmmax = kernel.shmall * PAGE_SIZE
	kernel.shmmax = 810810728448
	kernel.shmmni = 4096
	vm.overcommit_memory = 2
	vm.overcommit_ratio = 95
	net.ipv4.ip_local_port_range = 10000 65535
	kernel.sem = 250 2048000 200 8192
	kernel.sysrq = 1
	kernel.core_uses_pid = 1
	kernel.msgmnb = 65536
	kernel.msgmax = 65536
	kernel.msgmni = 2048
	net.ipv4.tcp_syncookies = 1
	net.ipv4.conf.default.accept_source_route = 0
	net.ipv4.tcp_max_syn_backlog = 4096
	net.ipv4.conf.all.arp_filter = 1
	net.ipv4.ipfrag_high_thresh = 41943040
	net.ipv4.ipfrag_low_thresh = 31457280
	net.ipv4.ipfrag_time = 60
	net.core.netdev_max_backlog = 10000
	net.core.rmem_max = 2097152
	net.core.wmem_max = 2097152
	vm.swappiness = 10
	vm.zone_reclaim_mode = 0
	vm.dirty_expire_centisecs = 500
	vm.dirty_writeback_centisecs = 100
	vm.dirty_background_ratio = 0
	vm.dirty_ratio = 0
	vm.dirty_background_bytes = 1610612736
	vm.dirty_bytes = 4294967296
	```

	##### Shared memory settings

	In the `/etc/sysctl.conf` configuration file, `kernel.shmall` represents the total amount of available shared memory, in pages. `kernel.shmmax` represents the maximum size of a single shared memory segment, in bytes.

	You can define these 2 values using the operating system's `_PHYS_PAGES` and `PAGE_SIZE` parameters:

	```
	kernel.shmall = ( _PHYS_PAGES / 2)
	kernel.shmmax = ( _PHYS_PAGES / 2) * PAGE_SIZE
	```

	To get the values of these 2 operating system parameters, you can use `getconf`, for example:

	```bash
	$echo $(expr $(getconf _PHYS_PAGES)/2)
	$echo $(expr $(getconf _PHYS_PAGES)/2 \*$(getconf PAGE_SIZE))
	```

	- `vm.overcommit_memory` indicates the overcommit handling modes for memory. Available options are:

	- `0`: Heuristic overcommit handling
	- `1`: Always overcommit
	- `2`: Don't overcommit

	Set the value of this parameter to `2` to refuse overcommit.

	- `vm.overcommit_ratio` is a kernel parameter and is the percentage of RAM occupied by the application process. The default value on CentOS is `50`. `vm.overcommit_ratio` is calculated as follows:

	```
	vm.overcommit_ratio = (RAM - 0.026 * gp_vmem) / RAM
	```

	- The calculation method of `gp_vmem` is as follows:

	```
	# If the system memory is less than 256 GB, use the following formula to calculate:
	gp_vmem = ((SWAP + RAM) – (7.5GB + 0.05 * RAM)) / 1.7

	# If the system memory is greater than or equal to 256 GB, use the following formula to calculate:
	gp_vmem = ((SWAP + RAM) – (7.5GB + 0.05 * RAM)) / 1.17

	# In the above formulas, SWAP is the swap space on the host, in GB.
	# RAM is the size of the memory installed on the host, in GB.
	```

	##### IP segmentation settings

	When the Apache Cloudberry uses the UDP protocol for internal connection, the network card controls the fragmentation and reassembly of IP packets. If the size of a UDP message is larger than the maximum size of network transmission unit (MTU), the IP layer fragments the message.

	- `net.ipv4.ipfrag_high_thresh`: When the total size of IP fragments exceeds this threshold, the kernel will attempt to reorganize IP fragments. If the fragments exceed this threshold but all fragments have not arrived within the specified time, the kernel will not reorganize the fragments. This threshold is typically used to control whether larger shards are reorganized. The default value is `4194304` bytes (4 MB).
	- `net.ipv4.ipfrag_low_thresh`: Indicates that when the total size of IP fragments is below this threshold, the kernel will wait as long as possible for more fragments to arrive, to allow for larger reorganizations. This threshold is used to minimize unfinished reorganization operations and improve system performance. The default value is `3145728` bytes (3 MB).
	- `net.ipv4.ipfrag_time` is a kernel parameter that controls the IP fragment reassembly timeout. The default value is `30`.

	It is recommended to set the above parameters to the following values:

	```
	net.ipv4.ipfrag_high_thresh = 41943040
	net.ipv4.ipfrag_low_thresh = 31457280
	net.ipv4.ipfrag_time = 60
	```

	##### System memory

	- If the server memory exceeds 64 GB, the following parameters are recommended in the `/etc/sysctl.conf ` configuration file:

	```
	vm.dirty_background_ratio = 0
	vm.dirty_ratio = 0
	vm.dirty_background_bytes = 1610612736 # 1.5GB
	vm.dirty_bytes = 4294967296 # 4GB
	```

	- If the server memory is less than 64 GB, you do not need to set `vm.dirty_background_bytes ` or `vm.dirty_bytes`. It is recommended to set the following parameters in the `/etc/sysctl.conf ` configuration file:

	```
	vm.dirty_background_ratio = 3
	vm.dirty_ratio = 10
	```

	- To deal with emergency situations when the system is under memory pressure, it is recommended to add the `vm.min_free_kbytes` parameter to the `/etc/sysctl.conf` configuration file to control the amount of available memory reserved by the system. It is recommended to set `vm.min_free_kbytes` to 3% of the system's physical memory, with the following command:

	```bash
	awk 'BEGIN {OFMT = "%.0f";} /MemTotal/ {print "vm.min_free_kbytes =", $2 * .03;}' /proc/meminfo /etc/sysctl.conf
	```

	- The setting of `vm.min_free_kbytes` is not recommended to exceed 5% of the system's physical memory.

	##### Resource limit

	Edit the `/etc/security/limits.conf` file and add the following content, which will limit the amount of hardware and software resources.

	```
	*soft nofile 524288
	*hard nofile 524288
	*soft nproc 131072
	*hard nproc 131072
	```

	##### CORE DUMP

	1. Add the following parameter to the `/etc/sysctl.conf` configuration file:

	```
	kernel.core_pattern=/var/core/core.%h.%t
	```

	2. Run the following command to make the configuration effective:

	```bash
	sysctl -p
	```

	3. Add the following parameter to `/etc/security/limits.conf`:

	```
	* soft core unlimited
	```

	##### Set mount options for the XFS file system

	XFS is the file system for the data directory of Apache Cloudberry. XFS has the following mount options:

	```
	rw,nodev,noatime,inode64
	```

	You can set up XFS file mounting in the `/etc/fstab` file. See the following commands. You need to choose the file path according to the actual situation:

	```bash
	mkdir -p /data0/
	mkfs.xfs -f /dev/vdc
	echo "/dev/vdc /data0 xfs rw,nodev,noatime,inode64 0 0" /etc/fstab
	mount /data0
	chown -R gpadmin:gpadmin /data0/
	```

	:::note
	The `nobarrier` option is not supported on RHEL 8/9 or Ubuntu systems. Use only the options `rw,nodev,noatime,inode64`.
	:::

	Run the following command to check whether the mounting is successful:

	```bash
	df -h
	```

	##### Blockdev value

	The blockdev value for each disk file should be `16384`. To verify the blockdev value of a disk device, use the following command:

	```bash
	sudo/sbin/blockdev --getra<devname>
	```

	For example, to verify the blockdev value of the example server disk:

	```bash
	sudo/sbin/blockdev --getra /dev/vdc
	```

	To modify the blockdev value of a device file, use the following command:

	```bash
	sudo/sbin/blockdev --setra<bytes> <devname>
	```

	For example, to modify the file blockdev value of the hard disk of the example server:

	```bash
	sudo/sbin/blockdev --setra16384/dev/vdc
	```

	##### I/O scheduling policy settings for disks

	The disk type, operating system, and scheduling policies of Apache Cloudberry are as follows:

	<table>
	<thead>
	<tr>
	<th>Storage device type</th>
	<th>OS</th>
	<th>Recommended scheduling policy</th>
	</tr>
	</thead>
	<tbody>
	<tr>
	<td rowspan="3">NVMe</td>
	</tr>
	<tr>
	<td>RHEL 8</td>
	<td>none</td>
	</tr>
	<tr>
	<td>Ubuntu</td>
	<td>none</td>
	</tr>
	<tr>
	<td rowspan="3">SSD</td>
	</tr>
	<tr>
	<td>RHEL 8</td>
	<td>none</td>
	</tr>
	<tr>
	<td>Ubuntu</td>
	<td>none</td>
	</tr>
	<tr>
	<td rowspan="3">Other</td>
	</tr>
	<tr>
	<td>RHEL 8</td>
	<td>mq-deadline</td>
	</tr>
	<tr>
	<td>Ubuntu</td>
	<td>mq-deadline</td>
	</tr>
	</tbody>
	</table>

	Refer to the following command to modify the scheduling policy. Note that this command is only a temporary modification, and the modification becomes invalid after the server is restarted.

	```bash
	echo schedulername>/sys/block/<devname>/queue/scheduler
	```

	For example, temporarily modify the disk I/O scheduling policy of the example server:

	```bash
	echo deadline>/sys/block/vdc/queue/scheduler
	```

	To permanently modify the scheduling policy, use the system utility `grubby`. After using `grubby`, the modification takes effect immediately after you restart the server. The sample command is as follows:

	```bash
	grubby --update-kernel=ALL --args="elevator=deadline"
	```

	To view the kernel parameter settings, use the following command:

	```bash
	grubby --info=ALL
	```

	##### Disable Transparent Huge Pages (THP)

	You need to disable Transparent Huge Pages (THP), because it reduces database performance. The command is as follows:

	```bash
	grubby --update-kernel=ALL --args="transparent_hugepage=never"
	```

	Check the status of THP:

	```bash
	cat /sys/kernel/mm/*transparent_hugepage/enabled
	```

	##### Disable IPC object deletion

	Disable IPC object deletion by setting the value of `RemoveIPC` to `no`. You can set this parameter in the `/etc/systemd/logind.conf` file of Apache Cloudberry.

	```
	RemoveIPC=no
	```

	After disabling it, run the following command to restart the server to make the disabling setting effective:

	```bash
	service systemd-logind restart
	```

	##### SSH connection threshold

	To set the SSH connection threshold, you need to modify the `MaxStartups` and `MaxSessions` parameters in the `/etc/ssh/sshd_config` configuration file. Both of the following writing methods are acceptable.

	```
	MaxStartups 200
	MaxSessions 200
	```

	```
	MaxStartups 10:30:200
	MaxSessions 200
	```

	Run the following command to restart the server to make the setting take effect:

	```bash
	service sshd restart
	```

	##### Clock synchronization

	Apache Cloudberry requires the clock synchronization to be configured for all hosts, and the clock synchronization service should be started when the host starts. You can choose one of the following synchronization methods:

	- Use the coordinator node's time as the source, and other hosts synchronize the clock of the coordinator node host.
	- Synchronize clocks using an external clock source.

	The example in this document uses an external clock source for synchronization, that is, adding the following configuration to the `/etc/chrony.conf` configuration file:

	```
	# Use public servers from the pool.ntp.org project.
	# Please consider joining the pool (http://www.pool.ntp.org/join.html).
	server 0.centos.pool.ntp.org iburst
	```

	After setting, you can run the following command to check the clock synchronization status:

	```bash
	systemctl status chronyd
	```

	### Step 2. Install Apache Cloudberry

	:::info
	Starting from Apache Cloudberry 2.1, RPM and DEB packages are officially provided. RPM packages support Rocky Linux 8/9, RHEL 8/9, and compatible distributions. DEB packages support Ubuntu 22.04.
	:::

	1. Download the package to the home directory of `gpadmin`.

	2. Install the package in the `/home/gpadmin` directory.

	When running the following command, you need to replace `<package path>` with the actual package path, as the `root` user. During the installation, the directory `/usr/local/cloudberry-db/` is automatically created.

	```bash
	cd /home/gpadmin

	# For RPM (Rocky Linux, RHEL, etc.)
	dnf install <RPM package path>
	# Or for older systems: yum install <RPM package path>

	# For DEB (Ubuntu)
	apt install <DEB package path>
	# Or alternatively: dpkg -i <DEB package path> && apt-get install -f
	```

	3. Grant the `gpadmin` user the permission to access the `/usr/local/cloudberry-db/` directory.

	```bash
	chown -R gpadmin:gpadmin /usr/local/cloudberry*
	```

	4. Configure local SSH connection for the node. As the `gpadmin` user, perform the following operations:

	```bash
	ssh-keygen
	ssh-copy-id localhost
	ssh `hostname` # Makes sure that the local SSH connection works well.
	```

	### Step 3. Deploy Apache Cloudberry with a single computing node

	Use the scripting tool [`gpdemo`](/docs/sys-utilities/gpdemo.md) to quickly deploy Apache Cloudberry. `gpdemo` is included in the RPM package and will be installed in the `GPHOME/bin` directory along with the configuration scripts (gpinitsystem, gpstart, and gpstop). `gpdemo` supports quickly deploying Apache Cloudberry with a single computing node.

	In the above [setting mount options for the XFS file system](#set-mount-options-for-the-xfs-file-system), the XFS file system's data directory is mounted on `/data0`. The following commands deploy a single-computing-node cluster in this data directory:

	```bash
	cd /data0
	NUM_PRIMARY_MIRROR_PAIRS=0 gpdemo # Uses gpdemo
	```

	When `gpdemo` is running, a warning will be output `[WARNING]: -SinglenodeMode has been enabled, no segment will be created.`, which indicates that Apache Cloudberry is currently being deployed in the single-computing-node mode.

	## Common issues

	### How to check the deployment mode of a cluster

	Perform the following steps to confirm the deployment mode of the current Apache Cloudberry cluster:

	1. Connect to the coordinator node.
	2. Execute `SHOW gp_role;` to view the operating mode of the cluster.

	- If `utility` is returned, it indicates that the cluster is in utility mode (maintenance mode), where only the coordinator node is available.

	Continue to run the `SHOW gp_internal_is_singlenode;` command to see whether the cluster is in the single-computing-node mode.

	- If `on` is returned, the current cluster is in the single-computing-node mode.
	- If `off` is returned, the current cluster is in utility maintenance mode.

	- If `dispatch` is returned, it means that the current cluster is a regular cluster containing segment nodes. You can further check the segment count, status, port, data directory, and other information of the cluster by running `SELECT * FROM n;`.

	### Where is the data directory

	`gpdemo` automatically creates a data directory in the current path (`$PWD`). For the single-computing-node deployment:

	- The default directory of the coordinator is `./datadirs/singlenodedir`.
	- The default directory of the coordinator standby node is `./datadirs/standby`.

	## How it works

	When you are deploying Apache Cloudberry in the single-computing-node mode, the deployment script `gpdemo` writes `gp_internal_is_singlenode = true` to the configuration file `postgresql.conf` and starts a coordinator and a coordinator standby node with the `gp_role = utility` parameter setting. All data is written locally without a segment or data distribution.

	## User-behavior changes

	In the single-computing-node mode, the product behavior of Apache Cloudberry has the following changes. You should pay attention to these changes before performing related operations:

	- When you execute `CREATE TABLE` to create a table, the `DISTRIBUTED BY` clause no longer takes effect. A warning is output: `WARNING: DISTRIBUTED BY clause has no effect in singlenode mode`.
	- The `SCATTER BY` clause of the `SELECT` statement is no longer effective. A warning is output: `WARNING: SCATTER BY clause has no effect in singlenode mode`.
	- Other statements that are not supported (for example, `ALTER TABLE SET DISTRIBUTED BY`) are declined with an error.
	- The lock level of `UPDATE` and `DELETE` statements will be reduced from `ExclusiveLock` to `RowExclusiveLock` to provide better concurrency performance, because there is only a single node without global transactions or global deadlocks. This behavior is consistent with PostgreSQL.