Thursday, January 1, 2015

Script to delete multipathed ASMLIB storage devices from Linux

Before storage device can be removed (or unassigned) from server, it must first be removed from Linux. This is even more necessary if the server is running Oracle ASMLib, because if there are any removed or read-only storage devices present when running service oracleasm scandisks, the command will just hang and server load will start to increase (maximum I've seen was 3500).

Here you find RedHat instructions on how to cleanly remove storage devices in RHEL6. A lot of steps, especially when running multipath and having multiple paths to each device.

Since we do database replication and cloning to test using storage replication, then assigning and unassigning storage devices from test servers is quite frequent and if not done properly and cleanly, we have to reboot the server. Here is a little script to help with that task. It takes ASMLib disk names to be removed as an argument, finds all paths to the device and removes them from Linux.

Tested in OEL5 (using RHEL kernel) and OEL6 (using UEK2 kernel). This script only deals with dm-* and sd* devices, so before using please check and modify the script for your environment. Before removing the storage devices from Linux, make sure that the disk groups are dismounted from ASM and they are not used.

Sunday, December 28, 2014

Sample code: Using the Oracle ZFS Storage Appliance REST API from Python

Most (all?) of the Oracle ZFS Storage Appliance (ZS3-4 in my case) management functions are also exposed through REST API so it is possible to script and automate the storage management tasks. No proprietary clients or GUI needed, just need to write a simple script that can send some REST commands over HTTPS to the appliance and parse the JSON output.

I had a task of automating test database refresh from production and part of that workflow is also cloning and attaching LUNs from ZFSSA. I did not find any sample code to access ZFSSA online, so here am I publishing my code. It is a Python script that makes a use of a few ZFSSA REST API calls and publishes them as Fabric tasks.

This script exposes four tasks:

  • clone - Creates a new clone from replication
  • attach_stage1 - Attaches all LUNs in a project to a single target server
  • attach_stage2 - Attaches all LUNs in a project to multiple target servers
  • drop - Deletes a project

ZFSSA REST API works fine if each LUN has only a single initiator group, but when assigning LUN to multiple initiator groups (to be used in a RAC setup), I observed the following errors (they must be ZFSSA REST API bugs):

  • When modifying LUN to be part of multiple initiator groups (PUT request to /api/storage/v1/pools/_poolname_/projects/_projectname_/luns/_lunname_), then the API responds with (argument numbers may be different): {"fault": {"message": "invalid input argument (assignednumber: invalid literal for int() with base 10: '0,0,0')", "code": 400, "name": "ERR_INVALID_ARG"}}. Nevertheless, ZFS GUI confirms that the operation was completed successfully. This script just ignores the returned error message, when assigning LUN to multiple initiator groups.
  • If any LUN in the project has multiple initiator groups defined, then API call to get the list of LUNs (GET request to /api/storage/v1/pools/_poolname_/projects/_projectname_/luns) in a project returns an error immediately: {"luns":[{"fault": {"message": "internal error", "code": 500, "name": "ERR_INTERNAL"}}]}. This script cannot reattach the LUNs in this case, since getting the list of LUNs fails.

Thursday, November 13, 2014

12c metadata only default values for NULL columns part 2

Yesterday I attended #cluboracle event in London (I highly recommend this event! ... but I don't recommend Thameslink train service :) ). In this event one interesting discussion popped up regarding 12c. I've already written about this feature, so in this post I'll clarify some points as I understand them and test out a few more things.

Here is a quote from my last post summing up my findings so far:

This new column seems to set a bit, whether the value in the column "should be trusted" or replaced with a default. So, all the rows that existed before the new column was added have NULL is this new column, but all the newly modified rows set a specific bit to 1. Looking at the original expression, then there is also a possibility that this bit is set to 0, maybe this newly added column can contain other "row status bits" also?

DECODE (TO_CHAR (sys_op_vecbit ("SYS_NC00003$", 0)),
    NULL, NVL ("DEF_W_NULL", 'THIS IS DEFAULT2'),
    '0', NVL ("DEF_W_NULL", 'THIS IS DEFAULT2'),
    '1', "DEF_W_NULL"
)

Therefore... Only the rows that existed previously don't have the default value written to the data blocks, all rows added after adding the column have the DEFAULT value written to the data block directly.. What happens if you update the old row?

SQL> create table default_values (
   id number primary key
  3  );

Table created.

SQL>  insert into default_values values (1);

1 row created.

SQL>  insert into default_values values (2);

1 row created.

SQL>  insert into default_values values (3);

1 row created.

SQL>  insert into default_values values (4);

1 row created.

SQL> alter table default_values add def_w_null varchar2(20) default 'THIS IS DEFAULT2';

Table altered.

SQL> insert into default_values (id) values (5);

1 row created.

SQL> commit;

Commit complete.

Here is the projection information for column DEF_W_NULL.

DECODE(TO_CHAR(SYS_OP_VECBIT("SYS_NC00002$",0)),
  NULL,NVL("DEF_W_NULL",'THIS IS DEFAULT2'),
  '0',NVL("DEF_W_NULL",'THIS IS DEFAULT2'),
  '1',"DEF_W_NULL")

The hidden column containing the bitmap in this test is SYS_NC00002$. Here is the current contents of this column and the interesting bit.

SQL> select id, DEF_W_NULL, nvl2(SYS_NC00002$,'is not null','is null') is_hidden_col_null, SYS_NC00002$, TO_CHAR (sys_op_vecbit(SYS_NC00002$,0)) bitval  FROM default_values;

        ID DEF_W_NULL           IS_HIDDEN_C SYS_NC00002$  BITVAL
---------- -------------------- ----------- ------------- --------
         1 THIS IS DEFAULT2     is null
         2 THIS IS DEFAULT2     is null
         3 THIS IS DEFAULT2     is null
         4 THIS IS DEFAULT2     is null
         5 THIS IS DEFAULT2     is not null 01            1

All as expected so far. ID 1-4 were added before adding the new column, so SYS_NC00002$ IS NULL for them and the NULL value in file is replaced with metadata default value. ID=5 was added after, so its BITVAL=1 and from the projection information we see, that this column is displayed how it is written to the file. What happens if I update ID=1 row but don't touch DEF_W_NULL column?

SQL> update default_values set id=10 where id=1;

1 row updated.

SQL> commit;

Commit complete.

SQL> select id, DEF_W_NULL, nvl2(SYS_NC00002$,'is not null','is null') is_hidden_col_null, SYS_NC00002$, TO_CHAR (sys_op_vecbit(SYS_NC00002$,0))bitval  FROM default_values;

        ID DEF_W_NULL           IS_HIDDEN_C SYS_NC00002$  BITVAL
---------- -------------------- ----------- ------------- --------
        10 THIS IS DEFAULT2     is null
         2 THIS IS DEFAULT2     is null
         3 THIS IS DEFAULT2     is null
         4 THIS IS DEFAULT2     is null
         5 THIS IS DEFAULT2     is not null 01            1

Nothing happened with DEF_W_NULL column, Oracle only updated ID column. What if I update DEF_W_NULL column first with keyword DEFAULT and then with the same value?

SQL> update default_values set def_w_null=default, id=11 where id=2;

1 row updated.

SQL> update default_values set def_w_null='THIS IS DEFAULT2', id=12 where id=3;

1 row updated.

SQL> commit;

Commit complete.

SQL> select id, DEF_W_NULL, nvl2(SYS_NC00002$,'is not null','is null') is_hidden_col_null, SYS_NC00002$, TO_CHAR (sys_op_vecbit(SYS_NC00002$,0))bitval  FROM default_values;

        ID DEF_W_NULL           IS_HIDDEN_C SYS_NC00002$  BITVAL
---------- -------------------- ----------- ------------- --------
        10 THIS IS DEFAULT2     is null
        11 THIS IS DEFAULT2     is not null 01            1
        12 THIS IS DEFAULT2     is not null 01            1
         4 THIS IS DEFAULT2     is null
         5 THIS IS DEFAULT2     is not null 01            1

Oracle has updated the physically stored value, so keep an eye on row migration possibilities!

What happens if I now change the default value in table metadata? Looking at the projection information it must update the existing rows to store the old default value. Lets verify.

SQL> alter table default_values modify DEF_W_NULL varchar2(20) default 'NEW DEFAULT';

Table altered.

SQL> insert into default_values (id) values (6);

1 row created.

SQL> commit;

Commit complete.

SQL> select id, DEF_W_NULL, nvl2(SYS_NC00002$,'is not null','is null') is_hidden_col_null, SYS_NC00002$, TO_CHAR (sys_op_vecbit(SYS_NC00002$,0))bitval  FROM default_values;

        ID DEF_W_NULL           IS_HIDDEN_C SYS_NC00002$  BITVAL
---------- -------------------- ----------- ------------- --------
        10 THIS IS DEFAULT2     is null
        11 THIS IS DEFAULT2     is not null 01            1
        12 THIS IS DEFAULT2     is not null 01            1
         4 THIS IS DEFAULT2     is null
         5 THIS IS DEFAULT2     is not null 01            1
         6 NEW DEFAULT          is not null 01            1

Whoa... really interesting. I didn't do anything! And I think it makes sense now also, it only has to store the initial DEFAULT value, when the column was not present in the table, rows added later already have the correct value written to the files. It must also mean, that Oracle stores two different default values in table metadata - the currently active default value and the initial value when column was added.

The last small thing I want to test, what if I have multiple columns with NULL default values in the same table, does it add one hidden column for each of them?

SQL> alter table default_values add def_w_null2 varchar2(20) default 'THIS IS DEFAULT 3';

Table altered.

SQL> insert into default_values (id) values (6);

1 row created.

SQL> commit;

Commit complete.

SQL> select id, DEF_W_NULL, nvl2(SYS_NC00002$,'is not null','is null') is_hidden_col_null, SYS_NC00002$, TO_CHAR (sys_op_vecbit(SYS_NC00002$,0))bitval1, TO_CHAR (sys_op_vecbit(SYS_NC00002$,1)) bitval2  FROM default_values where id in (6,7);

        ID DEF_W_NULL           IS_HIDDEN_C SYS_NC00002$  BITVAL1   BITVAL2
---------- -------------------- ----------- ------------- --------- ---------
         6 NEW DEFAULT          is not null 01            1         0
         7 NEW DEFAULT          is not null 03            1         1

The new column projection information:

DECODE(TO_CHAR(SYS_OP_VECBIT("SYS_NC00002$",1)),
  NULL,NVL("DEF_W_NULL2",'THIS IS DEFAULT 3'),
  '0',NVL("DEF_W_NULL2",'THIS IS DEFAULT 3'),
  '1',"DEF_W_NULL2")

I'm pleasantly surprised again! It did not add a new column, just used another bit in the same column.

Tuesday, November 4, 2014

Slides from OUGE Meetup #3

I gave a talk about my highlights from Oracle Open World 2014 and how to use CloneDB in Oracle User Group Estonia Meetup #3. It was a really good meetup and thanks to everybody who attended.

Here you can find the slides

Wednesday, October 29, 2014

Structured XML output from Oracle SQL query

Got an interesting question today: There are tables TABLE1, TABLE2 and a junction table that joins them called JUNCTABLE. Need the following output as XML


  
  


  
  

I know the output could be aggregated using XMLAGG, but I have never looked into how to format the tag names and attributed in the output like requested.

Data in my very simplified sample tables:

SQL> select * from table1;

        ID
----------
         1
         2
         3

SQL> select * from table2;

        ID
----------
        11
        12
        13
        14

SQL> select * from junctable;

     T1_ID      T2_ID
---------- ----------
         1         11
         1         12
         2         12
         2         13
         3         14

Expected output:

  
    
    
  
  
    
    
  
  
    
  

Now the query itself:

SELECT XMLAGG (xmlpieces)
  FROM (  SELECT XMLELEMENT ("table1", xmlattributes (t1.id AS "id"), 
                   XMLAGG (XMLELEMENT ("table2", xmlattributes (t2.id AS "id")))
                 ) xmlpieces
            FROM table1 t1
                 JOIN junctable j ON j.t1_id = t1.id
                 JOIN table2 t2 ON t2.id = j.t2_id
        GROUP BY t1.id);

And the result: