Merge pull request #89 from exasol/vshilin-IPS-503

Create creating_test_table_specified_mem_object_size.md

Database-Features/creating_test_table_specified_mem_object_size.md

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+# Creating a test table with a specified MEM_OBJECT_SIZE
+
+This article provides a detailed guide on using the `create_table_mem_object_size` script to create tables with a specified memory size (MEM_OBJECT_SIZE). It might be useful for Support investigations and experiments.
+
+To use the script, simply create it in your desired schema. Be careful if a table named "dummy" already exists as the script will recreate it. 
+The script is designed to create a target table where each row occupies 128 bytes, with randomly generated content ensuring the actual table mem size is 128 bytes times the number of rows. 
+The number of rows required to populate the target table is calculated based on the value of the parameter mem_object_size.
+To generate a potentially large target table, the script uses a cartesian join of a smaller manageable "dummy" table on itself, multiplying the record count to reach the desired size.   
+
+## script
+```sql
+create schema test_data_gen;
+open schema test_data_gen;
+
+--/
+create or replace script create_table_mem_object_size(
+        schema_name, table_name,  --target table schema/name
+        mem_object_size           --target table desired mem_object_size 
+        ) as 
+dummy_table_rows_cnt = (math.floor(math.sqrt(mem_object_size * 1024 * 1024 / 128))) + 1
+
+res1 = query([[
+DROP TABLE IF EXISTS dummy;
+]])
+
+res2 = query([[
+CREATE TABLE dummy as
+SELECT 1 AS dummy FROM dual CONNECT BY LEVEL <= ]] .. dummy_table_rows_cnt .. [[;
+]])
+
+res3 = query([[
+CREATE TABLE ]] .. schema_name .. '.' .. table_name .. [[ as
+SELECT 
+	RAND(1,100) AS rand1, 
+	RAND(1,100) AS rand2,
+	RAND(1,100) AS rand3,
+	RAND(1,100) AS rand4,
+	RAND(1,100) AS rand5,
+	RAND(1,100) AS rand6,
+	RAND(1,100) AS rand7,
+	RAND(1,100) AS rand8,
+	RAND(1,100) AS rand9,
+	RAND(1,100) AS rand10, 
+	RAND(1,100) AS rand11,
+	RAND(1,100) AS rand12,
+	RAND(1,100) AS rand13,
+	RAND(1,100) AS rand14,
+	RAND(1,100) AS rand15,
+	RAND(1,100) AS rand16
+
+	--each row takes 128 byte RAW
+FROM 
+(SELECT 1 from
+test_data_gen.dummy x1,
+test_data_gen.dummy x2);
+]])
+
+
+
+while true do
+
+    res = query([[commit]])
+    cur_size = query([[select mem_object_size/1024/1024 as MEM from exa_all_object_sizes where object_name = upper(']] .. table_name .. [[') and ROOT_NAME = upper(']] .. schema_name .. [[') ]])
+
+    if cur_size[1].MEM >= mem_object_size then
+        break;
+    end
+
+    curr_count = query([[select table_row_count as CNT from exa_all_tables where table_name = upper(']] .. table_name .. [[') and table_schema = upper(']] .. schema_name .. [[') ]])
+    local add_rows = curr_count[1].CNT * ( mem_object_size - cur_size[1].MEM) / cur_size[1].MEM
+    if add_rows < 100 then add_rows = 100 end 
+
+    res6 = query([[insert into ]] .. schema_name .. '.' .. table_name .. [[ select * from ]] .. schema_name .. '.' .. table_name .. [[ where rownum <= ]] .. add_rows)
+    output('Adding more rows to reach the target MEM_OBJECT ' .. add_rows)
+end
+/
+```
+
+## Examples
+
+1. 100Mb
+```sql
+drop table test_data_gen.tab_100mb;
+EXECUTE SCRIPT create_table_mem_object_size('test_data_gen', 'tab_100mb', 100);
+--2 second on a 4 node Saas cluster
+select mem_object_size/1024/1024 from exa_all_object_sizes where object_name = 'TAB_100MB' and ROOT_NAME = 'TEST_DATA_GEN'
+--result 105.32723617553710937500
+```
+
+2. 2Gb
+```sql
+drop table test_data_gen.tab_2gb;
+EXECUTE SCRIPT create_table_mem_object_size('test_data_gen', 'tab_2gb', 2048);
+--10 second on a 4 node Saas cluster
+select mem_object_size/1024/1024 from exa_all_object_sizes where object_name = 'TAB_2GB' and ROOT_NAME = 'TEST_DATA_GEN'
+--result 2048.02326202392578125000
+```
+
+3. 10Gb
+```sql
+drop table test_data_gen.TAB_10GB;
+EXECUTE SCRIPT create_table_mem_object_size('test_data_gen', 'tab_10gb', 10240);
+--35 seconds on a 4 node Saas cluster
+select mem_object_size/1024/1024 from exa_all_object_sizes where object_name = 'TAB_10GB' and ROOT_NAME = 'TEST_DATA_GEN'
+--result 10240.88970947265625000000
+```