{"id":9970,"date":"2017-04-21T19:47:20","date_gmt":"2017-04-21T17:47:20","guid":{"rendered":"https:\/\/www.dbi-services.com\/blog\/securefiles-on-multi-datafiles-tablespaces\/"},"modified":"2017-04-21T19:47:20","modified_gmt":"2017-04-21T17:47:20","slug":"securefiles-on-multi-datafiles-tablespaces","status":"publish","type":"post","link":"https:\/\/www.dbi-services.com\/blog\/securefiles-on-multi-datafiles-tablespaces\/","title":{"rendered":"SecureFiles on multi-datafiles tablespaces"},"content":{"rendered":"

By Franck Pachot<\/h2>\n

.
\nWhen we have a tablespace with multiple datafiles, we are used to seeing the datafiles filled evenly, the extents being allocated in a round-robin fashion. In the old time, we used that to maximize performance, distributing the tables to all disks. Today, we use LVM striping, maximum Inter-Policy, ASM even distribution. And we may even use bigfile tablespaces, so that we don’t care about having multiple datafiles.
\n
\nBut recently, during test phase of migration, I came upon something like this:
\n\"SecureFile003\"<\/a><\/p>\n

To reproduce the case, I’ve created a tablespace with 8 datafiles:<\/p>\n

\nSQL> create tablespace MYTABS datafile\n  2  '\/tmp\/MYTABS01.dbf' size 1M autoextend on maxsize 100M,\n  3  '\/tmp\/MYTABS02.dbf' size 1M autoextend on maxsize 100M,\n  4  '\/tmp\/MYTABS03.dbf' size 1M autoextend on maxsize 100M,\n  5  '\/tmp\/MYTABS04.dbf' size 1M autoextend on maxsize 100M,\n  6  '\/tmp\/MYTABS05.dbf' size 1M autoextend on maxsize 100M,\n  7  '\/tmp\/MYTABS06.dbf' size 1M autoextend on maxsize 100M,\n  8  '\/tmp\/MYTABS07.dbf' size 1M autoextend on maxsize 100M,\n  9  '\/tmp\/MYTABS08.dbf' size 1M autoextend on maxsize 100M\n 10  \/\n \nTablespace created.\n<\/code><\/pre>\n
SecureFiles<\/h3>\n
This was a 11g to 12c migration, with Data Pump, and a good occasion to convert all LOB to SecureFiles with the transform=lob_storage:securefile parameter. And this tablespace is the one where the LOB segments are stored. I reproduced it with:<\/p>\n
SQL> create table MYTABLE ( x clob ) tablespace USERS\n  2  LOB(x) store as securefile MYLOBSEG (tablespace MYTABS disable storage in row);\n \nTable created.\n<\/code><\/pre>\n
Then I inserted about 80MB:<\/p>\n
SQL> insert into MYTABLE select lpad('x',100000) from xmltable('1 to 8000') ;\n8000 rows created.\n \nSQL> select file_id,file_name,blocks,user_blocks from dba_data_files where tablespace_name='MYTABS' order by file_id;\n \n   FILE_ID FILE_NAME                          BLOCKS USER_BLOCKS\n---------- ------------------------------ ---------- -----------\n        61 \/tmp\/MYTABS01.dbf                     128         120\n        62 \/tmp\/MYTABS02.dbf                     128         120\n        63 \/tmp\/MYTABS03.dbf                     128         120\n        64 \/tmp\/MYTABS04.dbf                    9344        9336\n        65 \/tmp\/MYTABS05.dbf                     128         120\n        66 \/tmp\/MYTABS06.dbf                     128         120\n        67 \/tmp\/MYTABS07.dbf                     128         120\n        68 \/tmp\/MYTABS08.dbf                     128         120\n \n8 rows selected.\n \nSQL> select file_id,segment_type,sum(blocks) from dba_extents where tablespace_name='MYTABS' group by file_id,segment_type order by file_id,segment_type;\n \n   FILE_ID SEGMENT_TYPE       SUM(BLOCKS)\n---------- ------------------ -----------\n        64 LOBSEGMENT                9216\n        65 LOBINDEX                     8\n        65 LOBSEGMENT                  24\n<\/code><\/pre>\n
And I continued to load rows, and observed the datafiles filled to their maxsize one after the other, without numeric or alphabetical order.<\/p>\n
SQL> select file_id,file_name,blocks,user_blocks from dba_data_files where tablespace_name='MYTABS' order by file_id;\n \n   FILE_ID FILE_NAME                          BLOCKS USER_BLOCKS\n---------- ------------------------------ ---------- -----------\n        61 \/tmp\/MYTABS01.dbf                    8320        8312\n        62 \/tmp\/MYTABS02.dbf                   12416       12408\n        63 \/tmp\/MYTABS03.dbf                   12416       12408\n        64 \/tmp\/MYTABS04.dbf                   12416       12408\n        65 \/tmp\/MYTABS05.dbf                     128         120\n        66 \/tmp\/MYTABS06.dbf                     128         120\n        67 \/tmp\/MYTABS07.dbf                     128         120\n        68 \/tmp\/MYTABS08.dbf                     128         120\n \n8 rows selected.\n \nSQL> select file_id,segment_type,sum(blocks) from dba_extents where tablespace_name='MYTABS' group by file_id,segment_type order by file_id,segment_type;\n \n   FILE_ID SEGMENT_TYPE       SUM(BLOCKS)\n---------- ------------------ -----------\n        61 LOBSEGMENT                8192\n        62 LOBSEGMENT               12288\n        63 LOBSEGMENT               12288\n        64 LOBSEGMENT               12288\n        65 LOBINDEX                     8\n        65 LOBSEGMENT                  24<\/code><\/pre>\n
Here are some screenshots during this load<\/p>\n
\"SecureFile001\"<\/a><\/p>\n
\"SecureFile002\"<\/a><\/p>\n
\"SecureFile003\"<\/a><\/p>\n
BasicFiles<\/h3>\n
This occurs only with SecureFiles. With the same load into LOB stored as BasicFile I got the following distribution:
\n\"SecureFile004\"<\/a><\/p>\n
Note that the inserts to BasicFile were about two times slower than the same into SecureFiles. <\/p>\n
So what?<\/h3>\n
I don’t see any bad consequences about that, and this may even be an improvement when concurrent sessions are loading the LOBs. When the datafile picked-up looks random, a guess is that it depends on a process ID to try to distribute the concurrent load. And if you want to distribute data over multiple disks, then you should do it at a lower level. However, it is 30 years behavior that changes and it’s better to be aware of it: datafiles may reach their maxsize even when the tablespace is not full. I order to be sure that it is the expected behavior, I opened an SR with easy to reproduce testcase. Status is ‘review update’ for 9 days (SR 3-14677784041) and I’ll update this post is I get an answer.<\/p>\n","protected":false},"excerpt":{"rendered":"
By Franck Pachot . When we have a tablespace with multiple datafiles, we are used to seeing the datafiles filled evenly, the extents being allocated in a round-robin fashion. In the old time, we used that to maximize performance, distributing the tables to all disks. Today, we use LVM striping, maximum Inter-Policy, ASM even distribution. […]<\/p>\n","protected":false},"author":27,"featured_media":9972,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[198],"tags":[96,207],"type_dbi":[],"class_list":["post-9970","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-database-management","tag-oracle","tag-securefiles"],"acf":[],"yoast_head":"\nSecureFiles on multi-datafiles tablespaces - dbi Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.dbi-services.com\/blog\/securefiles-on-multi-datafiles-tablespaces\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"SecureFiles on multi-datafiles tablespaces\" \/>\n<meta property=\"og:description\" content=\"By Franck Pachot . When we have a tablespace with multiple datafiles, we are used to seeing the datafiles filled evenly, the extents being allocated in a round-robin fashion. In the old time, we used that to maximize performance, distributing the tables to all disks. Today, we use LVM striping, maximum Inter-Policy, ASM even distribution. 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