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HANA Memory Allocation Limit Change With hdbcons for HANA

The SAP HANA command line utility hdbcons can be used to administer the HANA system directly from the Linux operating system command line.

It’s a very powerful utility and I’m sure as time goes by, it will provide invaluable information and functionality for HANA DB administrators to help fine-tune the database.

Log in as the <sid>adm Linux user and run the hdbcons command.
It will automatically connect the indexserver for that instance (if it’s running).
You can then list the available server commands:

hana01:/usr/sap/H10/HDB10> hdbcons
SAP HANA DB Management Client Console (type ‘?’ to get help for client commands)
Try to open connection to server process ‘hdbindexserver’ on system ‘H10′, instance ’10’
SAP HANA DB Management Server Console (type ‘help’ to get help for server commands)
Executable: hdbindexserver (PID: 4092)

> help

Available commands:
ae_checksize – Check and Recalculate size of columns within the Column Store
authentication – Authentication management.
bye – Exit console client
cd – ContainerDirectory management
checktopic – CheckTopic management
cnd – ContainerNameDirectory management
context – Execution context management (i.e., threads)
converter – Converter management
crash – Crash management
crypto – Cryptography management (SSL/SAML/X509).
deadlockdetector – Deadlock detector.
debug – Debug management
distribute – Handling distributed systems
dvol – DataVolume management
ELF – ELF symbol resolution management
encryption – Persistence encryption management
event – Event management
exit – Exit console client
flightrecorder – Flight Recorder
help – Display help for a command or command list
log – Show information about logger and manipulate logger
mm – Memory management
monitor – Monitor view command
mproxy – Malloc proxy management
mutex – Mutex management
output – Command for managing output from the hdbcons
pageaccess – PageAccess management
page – Page management
pcm – Performance Counter Monitor management
profiler – Profiler
quit – Exit console client
replication – Monitor data and log replication
resman – ResourceManager management
runtimedump – Generate a runtime dump.
savepoint – Savepoint management
snapshot – Snapshot management
statisticsservercontroller – StatisticsServer internals
statreg – Statistics registry command
stat – Statistics management
tablepreload – Manage and monitor table preload
tracetopic – TraceTopic management
trace – Trace management
version – Version management
vf – VirtualFile management

For each of the above commands, additional help can be obtained by re-issuing “help” plus the command name e.g.:

> help mm

Synopsis: mm <subcommand> [options]: Memory management Available subcommands:
   – list|l [-spf] [-l <level>] [<allocator_name>]: List allocators recursively
      -C: work on composite allocators
      -s: Print some allocator statistics (use stat command for full stats)
      -p: Print also peak usage statistics
      -f: Print allocator flags
      -S: Sort output descending by total size
      -l <level>: Print at most <level> levels
   – flag|f [-C] <allocator_name> [-rsdt] <flag_set>: Set allocator flags
      -C: work on composite allocators
      -r: Set flags recursively
      -s: Set given flag(s), default
      -d: Delete given flag(s)
      -t: Toggle given flag(s)
      -a: Also apply changes to associated composite allocators (not allowed in context with ‘-C’)
   – info|i [-f] <address>: Show block information for a given address
      -f: Force block info, even if block not known
   – blocklist|bl [-rtsS] <allocator_name> [-l <count>]: List of allocated blocks in an allocator
      -C: work on composite allocators
      -r: Show blocks in sub-allocators recursively
      -s: Show also allocation stack traces, if known. Cannot be combined with optiont ‘-t’.
      -S: Show only blocks with known allocation stack traces. Cannot be combined with optiont ‘-t’.
      -t: Show top allocation locations sorted by used size (descending).
            Cannot be combined with options ‘-s’ or ‘-S’.
            The default number of printed locations is 10, this can be changed by ‘-l’ option.
      -l <count>: Limit to <count> locations. Valid only if combined with option ‘-t’. Unlimited in cas <count> = 0.
   – maplist|ml: List all mappings used by the allocator
   – mapcheck|mc [-sln]: Check all mappings used by the allocator
      -s: Also show all system mappings
      -l: Also show own mappings as in maplist
      -n: Suppress output of known alloc stack traces for unaccounted memory
   – mapexec|me [-u]: List all known executable module mappings
      -u: Update list of known executable modules
   – reserveallocator|reserveallocators: Print information about OOM Reserve Allocators
   – top [-C] [-sctr] [-l <count>] [-o <fn>] [<allocator_name>]: List top users of memory, <allocator_name> is needed except for option ‘-t’
      -C: work on composite allocators
      -s: Sort call stacks by used size (default)
      -c: Sort call stacks by call count
      -t: Throughput, sort nodes by sum of all allocations
      -r: work recursively also for all suballocators
      -l <count>: Only output top <count> stack traces (0=unlimited)
      -o <fn>: Specify output file name
   – callgraph|cg [-sctrk] [-l <count>] [-o <fn>] [<allocator_name>]: Generate call graph, <allocator_name> is needed except for option ‘-t’
      -C: work on composite allocators
      -s: Sort nodes by used size (default)
      -k: Ouput in kcachegrind format
      -c: Sort nodes by call count
      -t: Throughput, sort nodes by sum of all allocations
      -r: Work recursively also for all suballocators
      -d: Do full demangle (also parameters and template arguments)
      -l <count>: Only output top <count> functions (0=unlimited)
      -o <fn>: Specify output file name (for .dot graph)
   – resetusage|ru [-r] [<allocator_name>]: Reset call stack usage counters, <allocator_name> is needed except for option ‘-r’ or ‘-C’
      -C: work on composite allocators
      -r: Work recursively also for all suballocators
   – limit [-s <size>[K|M|G|T]]: Get current allocation limit in bytes
      -s <size>[K|M|G|T]: Set current allocation limit in bytes, KB, MB or GB
   – globallimit [-s <size>[K|M|G|T]]: get current global (if IPMM is active) allocation limit in bytes
      -s <size>[K|M|G|T]: Set current global (if IPMM is active) allocation limit in bytes, KB, MB or GB
   – garbagecollector|garbagecollection|gc [-f]: Return free segments/blocks to
     operating system
      -f: Also return free fragments in big blocks
   – ipmm: Print Inter Process Memory Management information
      -d: Print detailed information.
   – compactioninfo, ci: Print information about last compaction
   – virtual: Print information about virtual but not resident memory (linux only)
   – requested: Print information about requested allocations (reporting no overhead at all), iterates over all instances of ReportRequestedAllocators
   – blockedmemory [-s <size>[K|M|G|T]]: Get current blocked memory.
      -s <size>[K|M|G|T]: Set current blocked memory in bytes, KB, MB or GB and try to reserve this memory. Common options and arguments:
   – <allocator_name>: Name of the allocator to address
   – <flag_set>: Comma-separated list of following flags: ffence (fence front, writes the pattern 0xaaccaacc in front of the allocated block),
     bfence (fence back, writes the pattern 0xaaccaacc behind the allocated block), astrace (stack trace at allocation),
     dstrace (stack trace at deallocation), areset (overwrite at allocate with pattern 0xd00ffeed),
     dreset (overwrite at deallocate with pattern 0xdeadbeef), all, none, default, !emptyok (allow
     non-empty destruction), preventcheck (prevent changing check flags)
     atrace (trace at allocation), dtrace (trace at deallocation),
     malf (malfunction) or their 2-letter shortcuts [OK]


As an example, the current global allocation limit can be displayed:

> mm globallimit
Current global allocation limit=15032385536B.

We can adjust the global allocation limit online by issuing the additional “-s” parameter:

> mm globallimit -s 16G
Current global (if IPMM active) allocation limit: 17179869184B


Now re-check:

mm globallimit
Current global allocation limit=17179869184B.


What’s the current global allocation limit  in the global.ini you might ask?

hana01:/usr/sap/H10/HDB10> grep ‘^global’  /usr/sap/H10/SYS/global/hdb/custom/config/global.ini

global_allocation_limit = 14336

It hasn’t changed.

So we have confirmed that we can affect the configuration of the HANA system in real-time using hdbcons, but we don’t necessarily preserve the configuration.
You can also check in HANA Studio on the landscape page.
Since each service (process) takes it’s memory allocation percentage from the global allocation, this will automatically change in real-time too.
This means that for analysing “what-if” style scenarios or for operational acceptance testing, you can effectively present a set of configuration values and work through them almost automatically.  Invaluable for those test automation guys in the field.

9 thoughts on HANA Memory Allocation Limit Change With hdbcons for HANA

  1. Hello
    Many thanks for this block.

    I have a question.
    Does HANA always reserve your RAM up to the allocation limit?


    1. Hi Steve,
      No, HANA doesn’t reserve the memory. It expects to be able to have access to the memory quantity specified in the global allocation limit.
      See SAP note 1999997.

  2. Hello Darryl,
    please help me understand this.
    I have a server with 500GB RAM. A HANA DB and application server is installed on the server.
    Allocation limit is set to 500 GB.
    However, the operating system level always shows that only 5 GB is free.
    HANA DB only uses 250 GB and the SAP instance 50 GB.

    Where is the rest of RAM ?

    Many thanks

  3. Hi Darryl,

    Many thanks for your answer.
    I have a Server. On this Server is installed a HANA DB and SAP Netweaver.

    The Linux top command and transaction ST06 show that I only have 5 GB of free RAM space left.
    phys_memsize (for SAP) is set to 50 GB.
    Allocation_memory_limit of HANA database is set to 478 GB.

    HANA Cockpit displays the following:
    Used Memory: 100 GB is in used
    Resident memory: 256 GB is in used

    So there should actually be 214 GB of free memory in RAM 500 (RAM) – 256 (HANA) – 30 (SAP) = 214 GB.

    Where is 214 GB of RAM used for?

    Many thanks

    1. Hi Steve,

      If the server only has 500GB of RAM, then I would not advise setting the allocation limit of HANA to 478GB.
      Is your SAP Netweaver allocated 50GB or 30GB (you say both)?
      You will need at least 4GB for the operating system and maybe more for tools.

      My calculation is:
      500(RAM) – 50(SAP) – 4(O/S) = 450GB for HANA allocation limit (maximum).
      I would be tempted to leave some additional free memory, so maybe set allocation limit to 440GB.

      When you run “free” at the Linux command prompt, you will see that Linux has allocated all the memory.
      Linux tries to use any free memory as filesystem buffer.
      See here:
      It will tell you: Free Memory = ‘free’ + (‘buffers’ + ‘cached’)


  4. Hello Darryl

    Thanks very much.

    My SAP system has 30GB memory.

    Is an installation like mine (HANA DB and SAP Netweaver) recommended for a productive system at all? Or is it better to install the HANA database on a separate server (on a server where HANA runs alone)?

    My system should actually still have 214 GB RAM free.

    My calculation for free memory:
    RAM 500 (RAM) – 256 (HANA) – 30 (SAP) = 214GB.

    But free Command shows there is only 5GB free

    I do not understand where is the rest of RAM ?

    Thanks very much

  5. Hello Darryl,

    On the OS level (free -m) I get the following result.

    # free -m
    total used free shared buffers cached
    Mem: 806280 801157 5122 25748 3072 368940
    -/+ buffers/cache: 429144 377135
    Swap: 24575 17 24558

    On the SAP level (ST06) I get the following result.
    Memory: 800 GB
    Free Memory: 4 GB

    Why is there such a big difference ?
    Why does SAP only show 4 GB of free memory and 377 GB is still free on the Linux level?

    Many thanks

    1. Hi Steve,

      It’s the same issue that you saw at the Linux level. The reporting is not accurate.
      Have a look at SAP note 3044106 “Inconsistent Memory Statistics”. It’s possible your combination of SAP Netweaver, SAP Hostagent and Operating System is responsible.



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