alamb commented on issue #18909:
URL: https://github.com/apache/datafusion/issues/18909#issuecomment-3572864231
# Metadata caching study
Given the way the scripts run, the metadata cache is not used for each run.
I confirmed that metadata caching makes a pretty significant difference by
"prewarming" the cache by adding `select count(*) from hits;` to create.sql.
```shell
diff --git a/datafusion-partitioned/create.sql
b/datafusion-partitioned/create.sql
index 3b3330c1..a01baa64 100644
--- a/datafusion-partitioned/create.sql
+++ b/datafusion-partitioned/create.sql
@@ -2,3 +2,5 @@ CREATE EXTERNAL TABLE hits
STORED AS PARQUET
LOCATION 'partitioned'
OPTIONS ('binary_as_string' 'true');
+-- prewarm metadata cache
+select count(*) from hits;
diff --git a/datafusion-partitioned/run.sh b/datafusion-partitioned/run.sh
index 0c5ed184..74bcb0c2 100755
--- a/datafusion-partitioned/run.sh
+++ b/datafusion-partitioned/run.sh
@@ -11,11 +11,11 @@ cat queries.sql | while read -r query; do
echo -n "["
for i in $(seq 1 $TRIES); do
- # 1. there will be two query result, one for creating table another
for executing the select statement
- # 2. each query contains a "Query took xxx seconds", we just grep
these 2 lines
- # 3. use sed to take the second line
+ # 1. there will be three query result, one for creating table, one
to load metadata cache, and another for executing the select statement
+ # 2. each query contains a "Query took xxx seconds", we just grep
these 3 lines
+ # 3. use sed to take the third line
# 4. use awk to take the number we want
- RES=$(datafusion-cli -f create.sql /tmp/query.sql 2>&1 | grep
"Elapsed" |sed -n 2p | awk '{ print $2 }')
+ RES=$(datafusion-cli -f create.sql /tmp/query.sql 2>&1 | grep
"Elapsed" |sed -n 3p | awk '{ print $2 }')
[[ $RES != "" ]] && \
echo -n "$RES" || \
echo -n "null"
```
Making this change results in a 20% benchmark improvement for DataFusion 51
on c6a.4xlarge
<img width="1172" height="1307" alt="Image"
src="https://github.com/user-attachments/assets/b51218a7-3463-4fe4-b28c-5c785523a866";
/>
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