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I need help regarding LOAD-command with BLOBs.

I notice very poor performance while loading a table which contains large BLOBs. While tracing the OS, I only have about 15MB/sec I/O-speed. But in other cases I have normal I/O-rates > 200MB/sec. (e.g. creating DB-backups, creating tablespaces, copy files etc.).

I already tried to use different extent-sizes, page-sizes and some LOAD-parameters like "DISK_PARALLELISM", "SORT BUFFER", "DATA BUFFER", "SAVECOUNT" etc. to improve LOAD-performance but I was not able to speed up the LOAD. The target table is empty and has no indices defined. Source and target are located on separate RAID-volumes with dedicated physical drives.

Any hints to improve LOAD performance or to further investigate the problem are very welcome.

Thank you in advance.

Ronny

My setup:
- SLES 11 SP2
- DB2 9.7 FP8
- Raid: 
    Source: 2 dedicated Disks, Raid-0 (Striping) with 64 KB stripe-size
    Target: 2 dedicated Disks, Raid-0 (Striping) with 64 KB stripe-size
- File-System: EXT3
- Tablespace-Definition:
    CREATE LARGE TABLESPACE LOB IN DATABASE PARTITION GROUP IBMDEFAULTGROUP PAGESIZE 4096 MANAGED BY DATABASE USING (FILE 'xxx' 20000000) PREFETCHSIZE AUTOMATIC BUFFERPOOL IBMDEFAULTBP DROPPED TABLE RECOVERY OFF;

- LOAD-Definition:
    LOAD FROM xxx OF IXF LOBS FROM xxx MODIFIED BY lobsinfile METHOD N (ID, CONTENT, SEGMENTGROUPID, SEGMENTNUMBER) SAVECOUNT 1 ROWCOUNT 250 MESSAGES /xxx/CONTENT.log REPLACE INTO CONTENT (ID, CONTENT, SEGMENTGROUPID, SEGMENTNUMBER) NONRECOVERABLE;
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    So, you have a single logical volume that you're both reading and writing during the load? May be you should consider a separate device for the input data. Consider also creating a separate tablespace for LOBS with filesystem caching and create the data tablespace without filesystem caching.
    – mustaccio
    Jun 30 '14 at 14:31
  • Thank you for your hints. Source and target data resides on separate RAID-volumes. I use separate tablespaces for DATA and LOB Data. I will check the filesystem-chahing-options.
    – Ronny
    Jun 30 '14 at 14:36
  • Separate RAID volumes still sharing the same physical drives, I presume?
    – mustaccio
    Jun 30 '14 at 15:36
  • No, I use 4 HDDs altogeter; each raid-Volume uses 2 dedicated physical discs.
    – Ronny
    Jun 30 '14 at 15:55
  • Then it makes sense, of course, to put a completely different configuration in your question.
    – mustaccio
    Jun 30 '14 at 16:22
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As Chris already mentioned LOAD is a utility and therefore the UTIL_HEAP_SZ must be set high enough (but don't ask too much, always monitor the memory free space with top). You need a lot of memory for a fast load (see DATA BUFFER below).

Here are things that speed up the load:

  1. More containers for the tablespace where the table is (best on separate luns / disks)
  2. DATA BUFFER parameter (default 25% of UTIL_HEAP_SZ), make it bigger 400-800 (4K) per CPU core available.
  3. ANYORDER (allows LOAD to abandon the input order, bad if you load in clustering order) can give 30% boost
  4. FASTPARSE (use only if data is clean e.g. unloaded from other table) can give 15% boost
  5. SAVECOUNT - the higher the better I use #input records/10, so for 100M records the savecount is 10000000 - in your case 1 the LOAD has to update the restart data with every record = SLOW!

Note: always collect statistics with STATISTICS YES during load. It is faster than LOAD + RUNSTATS

Good luck and let us know your improvements!

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  • Thank You for your advices and the concrete expected effects - valuable information. But I already tried to improve performance using some of these parameters - without any countable effect in my scenario (lesser but much bigger entries due to BLOB columns). But in the meantime I discovered a solution, which speeds up the LOAD-performnce 8 times! I changed the pagesize of the affected LOB-tablespace to 32KB. I suppose, my problem is based in missing parallelism during loading BLOBs... For my scenario, the load performance is sufficient now. Thanks for all hints and information.
    – Ronny
    Jul 4 '14 at 10:00

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