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pg_dump for table with bytea takes a long time

On Database » PostgreSQL

2,881 words with 0 Comments; publish: Sat, 17 May 2008 22:08:00 GMT; (250125.00, « »)

I posted the following to the performance mailing list on 8/2/2005, but

have not heard any replies. Maybe this should just be a general

question. Would someone be able to help me get pb_dump to run faster

for bytea data?

++++++++++++++++++++++++++++++++++

Dumping a database which contains a table with a bytea column takes

approximately 25 hours and 45 minutes. The database has 26 tables in

it. The other 25 tables take less than 5 minutes to dump so almost all

time is spent dumping the bytea table.

prd1=# \d ybnet.ebook_master;

Table "ybnet.ebook_master"

Column | Type | Modifiers

--+--+--

region_key | integer | not null

book_key | integer | not null

pub_sequence | integer | not null

section_code | integer | not null

pagenbr | integer | not null

pdffile | bytea |

Indexes:

"ebook_master_pkey" PRIMARY KEY, btree (book_key, pub_sequence,

section_code, pagenbr, region_key)

Foreign-key constraints:

"FK1_book_year" FOREIGN KEY (book_key, pub_sequence, region_key)

REFERENCES ybnet.book_year(book_key, pub_sequence, region_key)

"FK1_ebook_section" FOREIGN KEY (section_code) REFERENCES

ybnet.ebook_section(sectioncode)

Tablespace: "ebook"

The tablespace ebook is 65504295 bytes in size and the ebook_master

table has 61-1GB files associated to it.

The command to dump the database is:

pg_dump --file=$DUMP_FILE --format=c --data-only --verbose

--host=ybcdrdbp01 $DATABASE

I also perform a hot backup of this database using pg_start_backup(),

tar, and pg_stop_backup(). It takes only 20 minutes to create a tar

ball of the entire 62GB. I like the speed of this method, but it does

not allow me to restore 1 table at a time.

The version of postgres is PostgreSQL 8.0.0 on i686-pc-linux-gnu,

compiled by GCC gcc (GCC) 3.2.2

The machine has 4 Xeon 3.00 GHz processors with hyper-threading on and

4GB of memory. Postgres is supported by two file systems connected to

an EMC SAN disk array. One 2 GB one for the log files and a second 500

GB one for the data and indexes. All output files for the backup files

are placed onto the 500 GB volume group and then backed up to an

external storage manager.

Portions of the config file are:

shared_buffers = 16384

work_mem = 8192

maintenance_work_mem = 16384

max_fsm_pages = 512000

max_fsm_relations = 1000

fsync = true

# - Checkpoints -

checkpoint_segments = 20

# - Planner Cost Constants -

effective_cache_size = 262144

random_page_cost = 3

I am looking for ideas for making the backup of the above table much

faster.

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