The following statement accesses an Object File System table from the compute cluster:
EXPLAIN SELECT * FROM ordertbl;
Explanation
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1) First, we lock ABENCH_OFS_1GB.ordertbl in TD_MAP1 for access on
a reserved RowHash to prevent global deadlock.
2) Next, we lock ABENCH_OFS_1GB.ordertbl in TD_MAP1 for access.
3) We MATERIALIZE ABENCH_OFS_1GB.ordertbl.
4) We do a single-AMP RETRIEVE step from root metadata of
ABENCH_OFS_1GB.ordertbl by way of an all-rows scan with no
residual conditions into Spool 6 (all_amps), which is
redistributed by the hash code of (
ABENCH_FS_1GB.ordertbl.Field_1028) to all AMPs in
td_compute_tiny_test. The size of Spool 6 is estimated with high
confidence to be 1 row (81 bytes). The estimated time for this
step is 0.26 seconds.
5) We do an all-AMPs RETRIEVE step in TD_COMPUTE_TINY_TEST from leaf
metadata of ABENCH_OFS_1GB.ordertbl
by way of external metadata in Spool 6 (Last Use) with no residual
conditions into Spool 7 (all_amps), which is redistributed by the
rowkey of (ABENCH_OFS_1GB.ordertbl.Field_1028) to all AMPs in
td_compute_tiny_test. Then we do a SORT to order Spool 7 by the sort
key as the field_id list( 4). The size of Spool 7 is estimated
with high confidence to be 8 rows (648 bytes). The estimated time
for this step is 0.02 seconds.
6) We do an all-AMPs BULK RETRIEVE step in TD_COMPUTE_TINY_TEST from
ABENCH_OFS_1GB.ordertbl by way of external metadata in Spool 7
(Last Use) with no residual conditions into Spool 1 (all_amps),
which is built locally on the AMPs. The size of Spool 1 is
estimated with low confidence to be 1,500,000 rows (132,000,000
bytes). The estimated time for this step is 1.89 seconds.
7) We do an all-AMPs RETRIEVE step in td_compute_tiny_test from Spool 1
(Last Use) by way of an all-rows scan into Spool 2 (all_amps),
which is built locally on the AMPs. The size of Spool 2 is
estimated with low confidence to be 1,500,000 rows (132,000,000
bytes). The estimated time for this step is 1.61 seconds.
8) We do an all-AMPs RETRIEVE step in td_compute_tiny_test from Spool 2
by way of an all-rows scan into Spool 3 (group_amps), which is
redistributed randomly to all AMPs in TD_Map1. The size of Spool
3 is estimated with low confidence to be 1,500,000 rows (
313,500,000 bytes).
9) Finally, we send out an END TRANSACTION step to all AMPs involved
in processing the request.
-> The contents of Spool 3 are sent back to the user as the result of
statement 1.