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SAP HANA Network Interview Questions and Answers for Experienced

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SAP HANA Network Interview Questions and Answers for Experienced
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SAP HANA Network FAQ

1. What is the meaning of network in the context of this SAP mean?

"Network" in the context of this SAP means all communications between different processes regardless of their distance and the kind of physical connection.

2. Which indications exist for SAP HANA network problems?

SQL: "HANA_Configuration_MiniChecks" (SAP s 1969700) returns a potentially critical issue (C = 'X') for one of the following individual checks:

Check ID Details
1510 Avg. intra node send throughput (MB/s)
1512 Avg. inter node send throughput (MB/s)
1520 Retransmitted TCP segments (%)
1522 Bad TCP segments (%)

See SAP 1999993 for more information related to SAP HANA Mini Checks.

A high amount of database threads are active with status 'Network Read' or 'Network Write' (see SAP 2114710).

3. What types of networks exist in SAP HANA environments?

The following main communication scenarios exist in SAP HANA environments:

SAP HANA Scenario Details Example
server intra-node Communication of a SAP HANA server process with another SAP HANA server process on the same host Topology request: indexserver <-> nameserver
server inter-node Communication of a SAP HANA server process with another SAP HANA server process on a different host Access to distributed table partitions: indexserver <-> indexserver
client / server Communication of a SAP HANA server process with a client process (SAP 2200772) ABAP workprocess request: indexserver (SQL executor thread) <-> SAP workprocess
system replication Communication between SAP HANA system replication sites (SAP 1999880) Synchronous log shipping from primary to secondary system

4. What are typical problems in the network area?

The following general areas are typically critical with respect to the network:

Area Details
Latency The latency or round trip time indicates how long it takes to send a request across the network. Latency is often an important performance factor in SAP HANA environments taking into account the efficient server processing due to column store and in memory.
Bandwidth The bandwidth defines the amount of data that can be transferred across network. if the bandwidth limit is reached, performance can drop dramatically.
Terminations Network related terminations can critically impact the availability and stability of SAP HANA.

5. How can I perform general network troubleshooting in SAP HANA environments?

See SAP 2081065 for troubleshooting general network problems in SAP HANA environments.

See SAP 1100926 for general remarks regarding network performance.

6. Are there specific network requirements for SAP HANA area?

The following documents describe network requirements for certain SAP HANA areas:

  • SAP HANA TDI - Network Requirements
  • Network Recommendations for SAP HANA System Replication

7. What are important network related SAP HANA parameters?

The following table lists important SAP HANA parameters related to the network:

Parameter Unit Network Area SAP Details
global.ini -> [communication] -> internal_network
 
server 2242514 Defines the internal network used for SAP HANA server process communication.
global.ini -> [communication] -> listeninterface
 
server 2183363 Controls how the SAP HANA server processes communicate with each other.
global.ini -> [internal_hostname_resolution] -> ...
 
server 2183363 Defines the SAP HANA internal host name resolution
global.ini -> [public_hostname_resolution] -> ...
 
server 2036111 Defines the SAP HANA public hostname resolution
global.ini -> [system_replication_hostname_resolution] -> ...
 
system replication 2183363 Defines the SAP HANA system replication host name resolution
global.ini -> [system_replication] -> enable_data_compression
 
system replication 1999880 (De-)activates compression of data being sent to secondary site
global.ini -> [system_replication] -> enable_log_compression
 
system replication 1999880 (De-)activates compression of log being sent to secondary site
indexserver.ini -> [distribution] -> client_distribution_mode
 
client / server 2200772 Controls to which SAP HANA scale-out node a specific client request connects
indexserver.ini -> [session] -> socket_keepalive
 
client / server 1836774 Controls dead connection detection
indexserver.ini -> [session] -> tcp_keepalive_time
s
client / server 1836774 Time between the last packet sent and the first dead connection detection probe
indexserver.ini -> [session] -> tcp_keepalive_intvl
s
client / server 1836774 Time between subsequent dead connection detection probes
indexserver.ini -> [session] -> tcp_keepalive_probes
 
client / server 1836774 Number of unacknowledged probes before reporting a dead connection
indexserver.ini -> [sql_client_network_io] -> buffer_size
rows
client / server 2119087 Defines the buffer size for the client network trace
indexserver.ini -> [sql_client_network_io] -> enabled
 
client / server 2119087 Controls the client network trace

8. What are SAP HANA errors related to network and communication?

The following table discusses common SAP HANA errors related to network communications. Be aware that sometimes the "2nd Level Error" messages cover quite similar aspects. If the recommendations for a specific "2nd Level Error" don't apply, you can therefore check for recommendations provided for similar errors related to the same main error.

Error 1st Level Error 2nd Level Error Details
-709 Cannot connect to VolumeID= Cannot connect to host : [Unknown host]

This error indicates that SAP HANA can't connect to a disk volume assigned to the specified SAP HANA host, because the host is not known. Check the network configuration and the availability of the host and the disk area in order to resolve this issue.

-813 Cannot connect to VolumeID= Cannot connect to host : [Connection refused]

This error indicates that SAP HANA can't connect to a disk volume assigned to the specified SAP HANA host, because the connection isn't accepted. Check the network configuration and the availability of the host and the disk area in order to resolve this issue.

-813 Cannot connect to VolumeID= Cannot connect to host : [Connection timed out]

This error indicates that SAP HANA can't connect to a disk volume assigned to the specified SAP HANA host, because the connection to the host times out. Check the network configuration and the availability of the host and the disk area in order to resolve this issue.

-10108 Session has been reconnected  

This error indicates that a connection / session to the SAP HANA server has been reconnected. Normally this should happen transparently without terminating the client transaction. Reasons for terminations are:

SAP Scenario Details
1964644 client Rev. <= 69.01 or 70

Bug in SAP HANA client, upgrade to newer client patch level

2090424 failover, client Rev. <= 84

Bug in SAP HANA client, upgrade to newer client patch level

-10709 Connection failed connect timeout expired

This error indicates that the defined connection timeout was reached. Typical reasons are:

SAP Scenario Details
2000000  

Connects running into timeouts can be caused by an issue on SAP HANA server side. Check the health on SAP HANA server side at the time of the error and make sure that it operates with a reasonable performance and without running in resource limitations.

2213725 ABAP

The connection timeout defined with the following parameter was exceeded:

dbs/hdb/connect_property = CONNECTTIMEOUT=

See SAP 2000003 for more information.

-10709 Connection failed no reachable host left

This error indicates that none of the SAP HANA server nodes configured on client side can be reached. Typical reasons are:

SAP Scenario Details

1882858

Data Services

Problems accessing odbc.ini file

1886746

BI

Inadequate ODBCINI environment setting
2077505

 

Port blocked by firewall
2090915

ABAP, BW

Deviation SAP HANA client vs. SAP HANA server release
2172036

ABAP

SAP HANA client bug, specify IP addresses rather than hostnames as a workaround or implement a SAP HANA client >= 85.05, 97.02 or 102.00
2213725   Problem with SAP HANA server, check state and trace files
2236989 ESP Inappropriate configuration of .odbc.ini file

 

-10709 Connection failed RTE:[89001] Cannot resolve host name '' rc=-3: Temporary failure in name resolution

This error indicates a problem in the host name resolution. Typical reasons are:

SAP Scenario Details
1828028   Wrong host name resolution settings on operating system level
-10709 Connection failed RTE:[89006] System call 'send' failed, rc=32:Broken pipe

This error indicates that the network pipe was terminated. Typical reasons are:

SAP Scenario Details
2213725   Check /var/log/messages for authentication issues, review hdbuserstore settings
-10709 Connection failed RTE:[89006] System call 'connect' failed, rc=111:Connection refused

This error indicates that a connection to the SAP HANA server is refused by the server or another component. Typical reasons are:

SAP Scenario Details
1828028 ABAP Incorrect hostname / port, database stopped or blocking firewall
1996048   Problem with host name resolution configuration
2089430 client Rev. <= 84
failover
Bug in SAP HANA client, upgrade to SAP HANA client >= 85
2168574 ABAP Wrong SSFS or hdbuserstore configuration
-10709 Connection failed RTE:[89006] System call 'connect' failed, rc=113:No route to host

This error indicates that the network stack isn't able to set up a route to the target host. Typical reasons are:

SAP Scenario Details
2130496 ABAP Wrong SSFS or hdbuserstore configuration
-10709 Connection failed RTE:[89006] System call 'connect' failed, rc=10060:A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond

This error indicates that a connection request didn't receive a response from the target host. Please check:

  • Client connection configuration (e.g. in SSFS or hdbuserstore)
  • Network settings (proper host name resolution and routing)
  • Availability of target host
-10709 Connection failed RTE:[89006] System call 'connect' failed, rc=10061:No connection could be made because the target machine actively refused it

This error indicates that a connection is refused by the target host. Typical reasons are:

SAP Scenario Details
1852017 ABAP Wrong SSFS or hdbuserstore configuration
-10709 Connection failed RTE:[89006] System call 'recv' failed, rc=104:Connection reset by peer

This error indicates that the remote host has dropped the network connection. Typical reasons are:

SAP Scenario Details
1771873   Inadequate nofile limitation using sapstartsrv
-10709 Connection failed RTE:[200107] Missing logon credential

This error indicates that no appropriate logon credentials were provided. Typical reasons are:

SAP Scenario Details
1830600 SUM Outdated SUM or SAP HANA version
-10807 System call 'recv' failed rc=104:Connection reset by peer

This error indicates that the target host can't be reached. Typical reasons are:

SAP Scenario Details
2089430 failover Expected termination of client connection after master node failover, triggers reconnect in ABAP environments (SAP 98051)
-10821 Session not connected  

This error indicates that a connection to SAP HANA doesn't exist, e.g. because it was never established successfully or because it terminated due to another error. In ABAP environments this error activates the reconnect mode (SAP 98051).

9. Which error codes activate the SAP ABAP reconnect mode?

The SAP ABAP reconnect mode is entered in order to avoid massive terminations and dumps in case of general database access issues (SAP 98051). The following error codes activate the reconnect mode:

-10708, -10709, -10715, 10807, -10821

10. Why the threads waiting long for the network?

Most usual call stacks of threads waiting for network requests are:

__read_nocancel
recv ()

If the threads appear to be stuck waiting for the network, Below is the following causes of this issue

SAP Re-examination Details
2338828 <= 112.03 If the connection is having M_CONNECTIONS.CONNECTION_STATUS = 'RECEIVING' and the call stack for the related thread contains Crypto::SSL::Filter::receive then the problem described in SAP 2338828 must be responsible: A runtime dump can cause network data packet loss when SSL is used.


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