Oracle Import Speed Performance Tips

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Oracle data load (import, SQL*Loader)

speed tips

Oracle Tips by Burleson Consulting

July 1, 2003 - Revised March 12, 2006

For professionals only: This is a expert-only overview of improving data pump import performance. For

beginners, see here. Also see my notes on tuning and improving Oracle export (expdp) performance

speed.

Maximizing Oracle Import (impdp) Performance

Regardless of which options were used when the data was exported, it has no influence on how the data is

imported. For example, it is irrelevant to the import process whether it was a direct path export or not,

since it is a plain export file, be it generated from direct or conventional means.

Unfortunately, there is no direct option available for imports (only for export and SQL*loader). The

import process has more tuning limitations than other utilities. The DBA should consider the following

when trying to optimize import performance:

Analyze once after the load - Set analyze=n and analyze with dbms_stats after the load has

completed.

Use Solid-state disk - For a fully-tuned import job, only faster devices can speed-up import rates.

Many large companies used partitioned tables, and keep the current partition on SSD for fast

imports.

Increase recordlength - Many set recordlength to 64k, but it needs to be a multiple of your I/O

chunk size and db_block_size (or your multiple block size, e.g. db_32k_block_size).

Set commit=n – For tables that can afford not to commit until the end of the load, this option

provides a significant performance increase. Larger tables may not be suitable for this option due to

the required rollback/undo space.

Dedicate a single, large rollback segment - Many professionals create a single large rollback

segment and take all others offline during the import.

Set indexes=n – Index creation can be postponed until after import completes, by specifying

indexes=n. If indexes for the target table already exist at the time of execution, import performs

index maintenance when data is inserted into the table. Setting indexes=n eliminates this

maintenance overhead. You can also use the indexfile=filename parm to rebuild all the indexes

once, after the data is loaded. When editing the indexfile, add the nologging and parallel keywords

(where parallel degree = cpu_count-1).

Set Sort parms - To speed-up index creation (as a separate import job), set sort_write_buffers=6,

sort_write_buffer_size=64000, sort_direct_write=true, and sort_area_size large enough prevent

disk sorts.

Defer CBO stats - Using impdp with the parameter exclude=statistics will greatly improve the

import speed, but statistics will need to be re-analyzed or imported later.

Use the buffer parameter – By using a larger buffer setting, import can do more work before disk

access is performed.

Disable logging - You can also use the hidden parameter _disable_logging = true to reduce redo,

but beware that the resulting import will be unrecoverable.

Import Option Elapsed Time

(Seconds)

Time

Reduction

commit=y 120 -

commit=y

buffer=64000

100 17%

Oracle Tips

database_properties tips

ORA 12899 Value too

Large for Column

ORA 27300 OS System

Dependent Operation

failed with status

ORA 01801 Date Format

is too Long for Internal

Buffer

ORA-00824: Cannot Set

sga_target Due to

Existing Internal Settings

Oracle import speed performance tips http://www.dba-oracle.com/oracle_tips_load_speed.htm

1 de 7 28/09/2011 22:55

Oracle Books

Oracle Scripts

Ion

Excel-DB

commit=n

buffer=30720

72 40%

commit=N

buffer = 64000

67 44%

Also see MOSC Note 155477.1 on improving importing speed:

You may be able to improve performance by increasing the value of the RECORDLENGTH parameter

when you invoke a direct path Export.

Your exact performance gain depends upon the following factors:

DB_BLOCK_SIZE

the types of columns in your table

your I/O layout (the drive receiving the export file should be separate from the disk

drive where the database files reside)

For example, invoking a Direct path Export with a maximum I/O buffer of 64kb can improve the

performance of the Export with almost 50%.

This can be achieved by specifying the additional Export parameters DIRECT and RECORDLENGTH.

e.g.:

exp userid=system/manager full=y direct=y recordlength=65535 file=exp_full.dmplog=exp_full.log

imp userid=system/manager full=y recordlength=65535 file=exp_full.dmplog=imp_full.log

Of all of the performance techniques for database loading, the most important is the nologging operation,

and the undocumented parameter _disable_logging=TRUE.

Note this discussion where Oracle expert Mark Bobak notes that you cannot re-start a failed instance

when using _disable_logging=true, and Don Burleson notes that _disable_logging should only be used

after taking a full, recoverable backup:

"The main things to consider about NOLOGGING:

Supported feature of Oracle

Works only with direct load insert

Still maintains minimal logging, i.e., space transactions, extent invalidation records

for loaded extents, etc.

Contrast with _disable_logging=TRUE:

Undocumented, unsupported parameter

all redo writes to log buffer still happen

writes of redo buffer down to disk are disabled.

Not limited to direct load insert. All operations are no longer protected by redo on

disk.

The big difference is, if your instance dies, (crash or shutdown abort) there's no data in the

online redo logs to even do instance recovery. This is very bad. Your database could suffer a

corruption from which you can't recover."

All experienced DBA's know that You MUST get approval from Oracle Technical Support for all usage of

undocumented parameters, but in the hands of a well-trained DBA, the hidden parameters are often a

Godsend, especially for speeding-up rebuilds during tight maintenance windows with limited downtime.

The backup sandwich:

Take a dump (full system backup)

Load everything I can in PARALLEL NOLOGGONG mode (ONLY during a scheduled downtime

window).

Take a dump. Take a full system backup right before bringing the system online.

Most DBA's call this high-speed maintenance a "backup sandwich", it's quite common in my world where

you have super-tight maintenance windows and every second counts.


2 de 7 28/09/2011 22:55

Remember, unless you take a full backup after your maintenance, using _disable_logging=TRUE, an

instance crash or a shutdown abort WILL trash your Oracle database.

Next, lets examine tips and techniques to improve the performance of all types of data loading, including

data pump import (impdp), sql*Loader and SQL INSERT DML.

Monitoring import performance

Monitoring Oracle Data Pump import performance is simple

select substr(sql_text,instr(sql_text,'into "'),30) table_name, rows_processed, round((sysdate-to_date(first_load_time,'yyyy-mm-dd hh24:mi:ss'))*24*60,1) minutes, trunc(rows_processed/((sysdate-to_date(first_load_time,'yyyy-mm-dd hh24:mi:ss'))*24*60)) rows_per_minutefrom sys.v_$sqlareawhere sql_text like 'insert %into "%' and command_type = 2 and open_versions > 0;

Maximizing SQL*Loader Performance

Oracle SQL*Loader is flexible and offers many options that should be considered to maximize the speed

of data loads. These include:

1. Use Direct Path Loads - The conventional path loader essentially loads the data by using

standard insert statements. The direct path loader (direct=true) loads directly into the Oracle

data files and creates blocks in Oracle database block format. The fact that SQL is not being

issued makes the entire process much less taxing on the database. There are certain cases,

however, in which direct path loads cannot be used (clustered tables). To prepare the

database for direct path loads, the script $ORACLE_HOME/rdbms/admin/catldr.sql.sql must

be executed.

2. Disable Indexes and Constraints. For conventional data loads only, the disabling of

indexes and constraints can greatly enhance the performance of SQL*Loader.

3. Use a Larger Bind Array. For conventional data loads only, larger bind arrays limit the

number of calls to the database and increase performance. The size of the bind array is

specified using the bindsize parameter. The bind array's size is equivalent to the number of

rows it contains (rows=) times the maximum length of each row.

4. Use ROWS=n to Commit Less Frequently. For conventional data loads only, rows

specifies the number of rows per commit. Issuing fewer commits will enhance performance.

5. Use Parallel Loads. Available with direct path data loads only, this option allows

multiple SQL*Loader jobs to execute concurrently.

$ sqlldr control=first.ctl parallel=true direct=true

$ sqlldr control=second.ctl parallel=true direct=true

6. Use Fixed Width Data. Fixed width data format saves Oracle some processing when

parsing the data. The savings can be tremendous, depending on the type of data and number

of rows.

7. Disable Archiving During Load. While this may not be feasible in certain environments,

disabling database archiving can increase performance considerably.

8. Use unrecoverable. The unrecoverable option (unrecoverable load data) disables the

writing of the data to the redo logs. This option is available for direct path loads only. Please

note that the UNRECOVERABLE option has been deprecated and replaced with the

NOLOGGING option.

Optimizing Oracle INSERT performance

The fastest Oracle table insert rate I've ever seen was 400,000 rows per second, about 24 millions rows per

minute, using super-fast RAM disk (SSD).

Speed of inserts is primarily a function of device speed, but NOLOGGING, maximum parallel DML

(which, in turn, a function of the number of CPU's and the layout of the disks) also factor into the

equation. When using standard SQL statements to load Oracle data tables, there are several tuning

approaches:

a - Manage segment header contention for parallel inserts - Make sure to define multiple

freelist (or freelist groups) to remove contention for the table header. Multiple freelists add

additional segment header blocks, removing the bottleneck. You can also use Automatic

Segment Space Management (bitmap freelists) to support parallel DML, but ASSM has some

limitations.


3 de 7 28/09/2011 22:55

b - Parallelize the load - You can invoke parallel DML (i.e. using the PARALLEL hint) to

have multiple inserts into the same table. For this INSERT optimization, make sure to define

multiple freelists or freelist groups. Mark Bobak notes that if you submit parallel jobs to insert

against the table at the same time, using the APPEND hint may cause serialization, removing

the benefit of parallel jobstreams.

c - APPEND into tables - By using the APPEND hint, you ensure that Oracle always grabs

"fresh" data blocks by raising the high-water-mark for the table. If you are doing parallel

insert DML, the Append mode is the default and you don't need to specify an APPEND hint.

Mark Bobak notes "Also, if you're going w/ APPEND, consider putting the table into

NOLOGGING mode, which will allow Oracle to avoid almost all redo logging."

Note: INSERT APPEND supports only the subquery syntax of the INSERT statement, not the VALUES clause.

insert /*+ append */ into customer (select xxx);

d - Use a large blocksize - By defining large (i.e. 32k) blocksizes for the target table, you

reduce I/O because more rows fit onto a block before a "block full" condition (as set by

PCTFREE) unlinks the block from the freelist.

e - Disable/drop indexes - It's far faster to rebuild indexes after the data load, all at-once. Also

indexes will rebuild cleaner, and with less I/O if they reside in a tablespace with a large block

size.

Using SSD for insert tablespaces

For databases that require high-speed loads, some shops define the insert table partition on solid-state disk

(later moving it to platter disk). Mike Ault notes in his book "Oracle Solid-State Disk Tuning", a

respectable 30% improvement in load speed:

“In the SSD verses ATA benchmark the gains for insert and update processing as shown in the

database loading and index build scenarios was a respectable 30%.I

This 30% was due to the CPU overhead involved in the insert and update activities.

If the Oracle level processing for insert and update activities could be optimized for SSD,

significant performance gains might be realized during these activities."

Import Speed Benchmarks:

Oracle guru Steve Callan notes that he has run parallel Data Pump import jobs to load 1.8 terabytes (1,800

gigabytes) in less than a day, an import load rate of over 75 gigabytes per hour.

“The target box was an AIX 5L using LPARS, pretty sure it was 32 CPU and 64GB RAM. There

were several distinct schemas, so the data pump export/import was a matter of divide and conquer

(i.e., stream several jobs/sessions). I think the largest chunk was around 900GB.

Statistics gathering took a while, but that time was separate from the actual import, and some

indexes were skipped/re-built later.

An old import version of this lasted right around three days, and the data pump version was about

a third of that time.”

As we see, the import speed is far greater using the newer Data Pump import utility (impdp) and imports

run faster of faster servers.

Also see:

Optimizing Oracle INSERT SQL performance

fast Oracle data load import sql*loader sqlldr data pump loading

Oracle Undocumented Utilities

Oracle9i RMAN Backup & Recovery OCP Preparation Class

Improving OLAP Performance in Oracle Database 10g Release 1

Oracle performance collection using vmstat

High Speed UNIX Oracle export import

Turning the Tables on Disk I/O with Oracle

Optimize Oracle import (data pump impdp) performance


4 de 7 28/09/2011 22:55

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Burleson Consulting does not partner with any SSD vendors and we provide independent advice in this

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Note: This Oracle documentation was created as a support and Oracle training

reference for use by our DBA performance tuning consulting professionals.

Feel free to ask questions on our Oracle forum.

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Oracle Import Speed Performance Tips