Not a DBA, need some assistance,

1) I am looking into possibilities to tune my parallel job processes. I have read to look into the pga_aggregate_size. Presently the size of PGA_aggregate_size is set to 125GB (the avilable memory in the box is 228GB).

Total 100 connections are processing parallel jobs and are waiting on PX Deq Credit: send blkd.

Do you think the value set to pga_aggregate_size is correct? Any suggestions.

2) in 10g, I can not see any value set to my db_cache_size or shared_pool_size. Is it ok? For your reference I am pasting parameter details below ..

------------------------------------ ----------- bitmap_merge_area_size integer 1048576
create_bitmap_area_size integer 8388608
db_16k_cache_size big integer 0
db_2k_cache_size big integer 0
db_32k_cache_size big integer 0
db_4k_cache_size big integer 0
db_8k_cache_size big integer 0
db_block_size integer 8192
db_cache_size big integer 0
db_keep_cache_size big integer 0
db_recovery_file_dest_size big integer 2G
db_recycle_cache_size big integer 0
global_context_pool_size string
hash_area_size integer 131072
java_max_sessionspace_size integer 0
java_pool_size big integer 0
large_pool_size big integer 0
max_dump_file_size string UNLIMITED
object_cache_max_size_percent integer 10
object_cache_optimal_size integer 102400
olap_page_pool_size big integer 0
parallel_execution_message_size integer 2152
sga_max_size big integer 44128M
shared_pool_reserved_size big integer 184M
shared_pool_size big integer 0
sort_area_retained_size integer 0
sort_area_size integer 65536
streams_pool_size big integer 0
workarea_size_policy string AUTO

Any help will be sincerely appreciated. Would like to reduce the PX Deq Credit: send blkd.