Mostafa Mokhtar created HIVE-9647:
-------------------------------------
Summary: Discrepancy in CBO between partitioned and un-partitioned
tables
Key: HIVE-9647
URL: https://issues.apache.org/jira/browse/HIVE-9647
Project: Hive
Issue Type: Bug
Components: CBO
Affects Versions: 0.14.0
Reporter: Mostafa Mokhtar
Assignee: Gunther Hagleitner
Fix For: 1.2.0
High-level summary
HiveRelMdSelectivity.computeInnerJoinSelectivity relies on per column number of
distinct value to estimate join selectivity.
The way statistics are aggregated for partitioned tables results in discrepancy
in number of distinct values which results in different plans between
partitioned and un-partitioned schemas.
The table below summarizes the NDVs in computeInnerJoinSelectivity which are
used to estimate selectivity of joins.
{code}
Column Partitioned count distincts Un-Partitioned count distincts
sr_customer_sk 71,245 1,415,625
sr_item_sk 38,846 62,562
sr_ticket_number 71,245 34,931,085
ss_customer_sk 88,476 1,415,625
ss_item_sk 38,846 62,562
ss_ticket_number 100,756 56,256,175
{code}
The discrepancy is because NDV calculation for a partitioned table assumes that
the NDV range is contained within each partition and is calculates as "select
max(NUM_DISTINCTS) from PART_COL_STATS” .
This is problematic for columns like ticket number which are naturally
increasing with the partitioned date column ss_sold_date_sk.
Suggestions
Use Hyper Log Log as suggested by Gopal, there is an HLL implementation for
HBASE co-porccessors which we can use as a reference here
Using the global stats from TAB_COL_STATS and the per partition stats from
PART_COL_STATS extrapolate the NDV for the qualified partitions as in :
Max ( (NUM_DISTINCTS from TAB_COL_STATS) x (Number of qualified partitions) /
(Number of Partitions), max(NUM_DISTINCTS) from PART_COL_STATS))
More details
While doing TPC-DS Partitioned vs. Un-Partitioned runs I noticed that many of
the plans are different, then I dumped the CBO logical plan and I found that
join estimates are drastically different
Unpartitioned schema :
{code}
2015-02-10 11:33:27,624 DEBUG [main]: parse.SemanticAnalyzer
(SemanticAnalyzer.java:apply(12624)) - Plan After Join Reordering:
HiveProjectRel(store_sales_quantitycount=[$0], store_sales_quantityave=[$1],
store_sales_quantitystdev=[$2], store_sales_quantitycov=[/($2, $1)],
as_store_returns_quantitycount=[$3], as_store_returns_quantityave=[$4],
as_store_returns_quantitystdev=[$5], store_returns_quantitycov=[/($5, $4)]):
rowcount = 1.0, cumulative cost = {6.056835407771381E8 rows, 0.0 cpu, 0.0 io},
id = 2956
HiveAggregateRel(group=[{}], agg#0=[count($0)], agg#1=[avg($0)],
agg#2=[stddev_samp($0)], agg#3=[count($1)], agg#4=[avg($1)],
agg#5=[stddev_samp($1)]): rowcount = 1.0, cumulative cost =
{6.056835407771381E8 rows, 0.0 cpu, 0.0 io}, id = 2954
HiveProjectRel($f0=[$4], $f1=[$8]): rowcount = 40.05611776795562,
cumulative cost = {6.056835407771381E8 rows, 0.0 cpu, 0.0 io}, id = 2952
HiveProjectRel(ss_sold_date_sk=[$0], ss_item_sk=[$1],
ss_customer_sk=[$2], ss_ticket_number=[$3], ss_quantity=[$4], sr_item_sk=[$5],
sr_customer_sk=[$6], sr_ticket_number=[$7], sr_return_quantity=[$8],
d_date_sk=[$9], d_quarter_name=[$10]): rowcount = 40.05611776795562, cumulative
cost = {6.056835407771381E8 rows, 0.0 cpu, 0.0 io}, id = 2982
HiveJoinRel(condition=[=($9, $0)], joinType=[inner]): rowcount =
40.05611776795562, cumulative cost = {6.056835407771381E8 rows, 0.0 cpu, 0.0
io}, id = 2980
HiveJoinRel(condition=[AND(AND(=($2, $6), =($1, $5)), =($3, $7))],
joinType=[inner]): rowcount = 28880.460910696, cumulative cost = {6.05654559E8
rows, 0.0 cpu, 0.0 io}, id = 2964
HiveProjectRel(ss_sold_date_sk=[$0], ss_item_sk=[$2],
ss_customer_sk=[$3], ss_ticket_number=[$9], ss_quantity=[$10]): rowcount =
5.50076554E8, cumulative cost = {0.0 rows, 0.0 cpu, 0.0 io}, id = 2920
HiveTableScanRel(table=[[tpcds_bin_orc_200.store_sales]]):
rowcount = 5.50076554E8, cumulative cost = {0}, id = 2822
HiveProjectRel(sr_item_sk=[$2], sr_customer_sk=[$3],
sr_ticket_number=[$9], sr_return_quantity=[$10]): rowcount = 5.5578005E7,
cumulative cost = {0.0 rows, 0.0 cpu, 0.0 io}, id = 2923
HiveTableScanRel(table=[[tpcds_bin_orc_200.store_returns]]):
rowcount = 5.5578005E7, cumulative cost = {0}, id = 2823
HiveProjectRel(d_date_sk=[$0], d_quarter_name=[$15]): rowcount =
101.31622746185853, cumulative cost = {0.0 rows, 0.0 cpu, 0.0 io}, id = 2948
HiveFilterRel(condition=[=($15, '2000Q1')]): rowcount =
101.31622746185853, cumulative cost = {0.0 rows, 0.0 cpu, 0.0 io}, id = 2946
HiveTableScanRel(table=[[tpcds_bin_orc_200.date_dim]]): rowcount
= 73049.0, cumulative cost = {0}, id = 2821
{code}
Partitioned schema :
{code}
2015-02-10 11:32:16,880 DEBUG [main]: parse.SemanticAnalyzer
(SemanticAnalyzer.java:apply(12624)) - Plan After Join Reordering:
HiveProjectRel(store_sales_quantitycount=[$0], store_sales_quantityave=[$1],
store_sales_quantitystdev=[$2], store_sales_quantitycov=[/($2, $1)],
as_store_returns_quantitycount=[$3], as_store_returns_quantityave=[$4],
as_store_returns_quantitystdev=[$5], store_returns_quantitycov=[/($5, $4)]):
rowcount = 1.0, cumulative cost = {6.064175958973647E8 rows, 0.0 cpu, 0.0 io},
id = 2791
HiveAggregateRel(group=[{}], agg#0=[count($0)], agg#1=[avg($0)],
agg#2=[stddev_samp($0)], agg#3=[count($1)], agg#4=[avg($1)],
agg#5=[stddev_samp($1)]): rowcount = 1.0, cumulative cost =
{6.064175958973647E8 rows, 0.0 cpu, 0.0 io}, id = 2789
HiveProjectRel($f0=[$3], $f1=[$8]): rowcount = 100840.08570910375,
cumulative cost = {6.064175958973647E8 rows, 0.0 cpu, 0.0 io}, id = 2787
HiveProjectRel(ss_item_sk=[$4], ss_customer_sk=[$5],
ss_ticket_number=[$6], ss_quantity=[$7], ss_sold_date_sk=[$8], sr_item_sk=[$0],
sr_customer_sk=[$1], sr_ticket_number=[$2], sr_return_quantity=[$3],
d_date_sk=[$9], d_quarter_name=[$10]): rowcount = 100840.08570910375,
cumulative cost = {6.064175958973647E8 rows, 0.0 cpu, 0.0 io}, id = 2817
HiveJoinRel(condition=[AND(AND(=($5, $1), =($4, $0)), =($6, $2))],
joinType=[inner]): rowcount = 100840.08570910375, cumulative cost =
{6.064175958973647E8 rows, 0.0 cpu, 0.0 io}, id = 2815
HiveProjectRel(sr_item_sk=[$1], sr_customer_sk=[$2],
sr_ticket_number=[$8], sr_return_quantity=[$9]): rowcount = 5.5578005E7,
cumulative cost = {0.0 rows, 0.0 cpu, 0.0 io}, id = 2758
HiveTableScanRel(table=[[tpcds_bin_partitioned_orc_200_orig.store_returns]]):
rowcount = 5.5578005E7, cumulative cost = {0}, id = 2658
HiveJoinRel(condition=[=($5, $4)], joinType=[inner]): rowcount =
762935.5811373093, cumulative cost = {5.500766553162274E8 rows, 0.0 cpu, 0.0
io}, id = 2801
HiveProjectRel(ss_item_sk=[$1], ss_customer_sk=[$2],
ss_ticket_number=[$8], ss_quantity=[$9], ss_sold_date_sk=[$22]): rowcount =
5.50076554E8, cumulative cost = {0.0 rows, 0.0 cpu, 0.0 io}, id = 2755
HiveTableScanRel(table=[[tpcds_bin_partitioned_orc_200_orig.store_sales]]):
rowcount = 5.50076554E8, cumulative cost = {0}, id = 2657
HiveProjectRel(d_date_sk=[$0], d_quarter_name=[$15]): rowcount =
101.31622746185853, cumulative cost = {0.0 rows, 0.0 cpu, 0.0 io}, id = 2783
HiveFilterRel(condition=[=($15, '2000Q1')]): rowcount =
101.31622746185853, cumulative cost = {0.0 rows, 0.0 cpu, 0.0 io}, id = 2781
HiveTableScanRel(table=[[tpcds_bin_partitioned_orc_200_orig.date_dim]]):
rowcount = 73049.0, cumulative cost = {0}, id = 2656
{code}
This was puzzling knowing that the stats for both tables are “identical” in
TAB_COL_STATS.
Column statistics from TAB_COL_STATS, notice how the column statistics are
identical in both cases.
{code}
DB_NAME COLUMN_NAME COLUMN_TYPE NUM_NULLS LONG_HIGH_VALUE
LONG_LOW_VALUE MAX_COL_LEN NUM_DISTINCTS
tpcds_bin_orc_200 d_date_sk int 0 2,488,070
2,415,022 NULL 65,332
tpcds_bin_partitioned_orc_200 d_date_sk int 0 2,488,070
2,415,022 NULL 65,332
tpcds_bin_orc_200 d_quarter_name string 0 NULL NULL 6
721
tpcds_bin_partitioned_orc_200 d_quarter_name string 0 NULL NULL
6 721
tpcds_bin_orc_200 sr_customer_sk int 1,009,571 1,600,000
1 NULL 1,415,625
tpcds_bin_partitioned_orc_200 sr_customer_sk int 1,009,571
1,600,000 1 NULL 1,415,625
tpcds_bin_orc_200 sr_item_sk int 0 48,000 1 NULL
62,562
tpcds_bin_partitioned_orc_200 sr_item_sk int 0 48,000 1
NULL 62,562
tpcds_bin_orc_200 sr_ticket_number int 0 48,000,000
1 NULL 34,931,085
tpcds_bin_partitioned_orc_200 sr_ticket_number int 0
48,000,000 1 NULL 34,931,085
tpcds_bin_orc_200 ss_customer_sk int 12,960,424 1,600,000
1 NULL 1,415,625
tpcds_bin_partitioned_orc_200 ss_customer_sk int 12,960,424
1,600,000 1 NULL 1,415,625
tpcds_bin_orc_200 ss_item_sk int 0 48,000 1 NULL
62,562
tpcds_bin_partitioned_orc_200 ss_item_sk int 0 48,000 1
NULL 62,562
tpcds_bin_orc_200 ss_sold_date_sk int 0 2,452,642
2,450,816 NULL 2,226
tpcds_bin_partitioned_orc_200 ss_sold_date_sk int 0 2,452,642
2,450,816 NULL 2,226
tpcds_bin_orc_200 ss_ticket_number int 0 48,000,000
1 NULL 56,256,175
tpcds_bin_partitioned_orc_200 ss_ticket_number int 0
48,000,000 1 NULL 56,256,175
{code}
For partitioned tables we get the statistics using get_aggr_stats_for which
eventually issues the query below
{code}
select
COLUMN_NAME,
COLUMN_TYPE,
…
max(NUM_DISTINCTS),
…
from
PART_COL_STATS
Where
where
DB_NAME =
and TABLE_NAME =
and COLUMN_NAME in
and PARTITION_NAME in (1 … N)
group by COLUMN_NAME , COLUMN_TYPE;
{code}
…
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