Oakies Blog Aggregator

https://ardentperf.files.wordpress.com/2019/03/hands-on-lab.jpg?w=600&h=450 600w, https://ardentperf.files.wordpress.com/2019/03/hands-on-lab.jpg?w=150&h=113 150w" sizes="(max-width: 300px) 100vw, 300px" />It feels like PostgresConf in New York is in full swing, even though the main tracks haven’t even started yet!

(Oh, and by the way, as of this morning I heard there are still day-passes available for those who haven’t yet registered for the conference… and then you can come hear a great session about Wait Events in PostgreSQL this Thursday at 4:20pm!)

The first two days of PostgresConf are summits, tutorials and training sessions. A good chunk of my day today was helping out with Scott Mead’s intensive 3 hour hands-on lab Setting up PostgreSQL for Production in AWS – but outside of that I’ve managed to drop in to a number of other sessions that sounded interesting. I did my best to take down some notes so I could share a few highlights.

Monday March 18

Personally, my favorite session on Monday was Brent Bigonger’s session.  He’s a database engineer at Amazon who was involved in migrating their Inventory Management System to Aurora PostgreSQL. I always love hearing good stories (part of why I’ve always been a fan of user groups) – this presentation gave a nice high level overview of the business, a review of the planning and execution process for the migration, and lots of practical lessons learned.

• Some of the tips were things people are generally familiar with – like NULLs behaving differently and the importance of performance management with a tool like Performance Insights.
• My favorite tip is getting better telemetry by instrumenting SQL with comments (SELECT /* my-service-call-1234 */ …) which reminded me of something I also read in Baron Sc​hwartz’s recently updated e-book on observable systems: “including implicit data in SQL.”
• A great new tip (to me) was the idea of creating a heartbeat table as one more safety check in a replication process.  You can get a sense for lag by querying the table and you can also use it during a cutover to get an extra degree of assurance that no data was missed.
• Another general point I really resonated with: Brent gave a nice reminder that a simple solution which meets the business requirements is better than a sophisticated or complex solution that goes beyond what the business really needs.  I feel tempted on occasion to leverage architectures because they are interesting – and I always appreciate hearing this reiterated!

On the AWS track, aside from Brent’s session, I caught a few others: Jim Mlodgenski giving a deep dive on Aurora PostgreSQL architecture and Jim Finnerty giving a great talk on Aurora PostgreSQL performance tuning and query plan management.  It’s funny, but I think my favorite slide from Finnerty’s talk was actually one of the simplest and most basic; he had a slide that just had high-level list of steps for performance tuning.  I don’t remember the exact list on that slide at the moment, but the essential process: (1) identify to top SQL (2) EXPLAIN to get the plan (3) make improvements to the SQL and (4) test and verify whether the improvements actually had the intended effect.

Other sessions I dropped into:

• Alvaro Hernandez giving an Oracle to PostgreSQL Migration Tutorial.  I love live demos (goes along with loving hands on labs) and so this session was a hit with me – I wasn’t able to catch the whole thing but I did catch a walk-through of ora2pg.
• Avinash Vallarapu giving an Introduction to PostgreSQL for Oracle and MySQL DBAs. When I slipped in, he was just wrapping up a section on hot physical backups in PostgreSQL with the pg_basebackup utility.  After that, Avi launched into a section on MVCC in PostgreSQL – digging into transaction IDs and vacuum, illustrated with block dumps and the pageinspect extension.  The part of this session I found most interesting was actually a few of the participant discussions – I heard lively discussions about what extensions are and about comparisons with RMAN and older versions of Oracle.

Tuesday March 19

As I said before, a good chunk of my morning was in Scott’s hands-on lab. If you ever do a hands-on lab with Scott then you’d better look out… he did something clever there: somewhere toward the beginning, if you followed the instructions correctly, then you would be unable to connect to your database!  Turns out this was on purpose (and the instructions actually tell you this) – since people often have this particular problem connecting when they first start on out RDS, Scott figured he’d just teach everyone how to fix it.  I won’t tell you what the problem actually is though – you’ll have to sign up for a lab sometime and learn for yourself.  :)

As always, we had a lot of really interesting discussions with participants in the hands-on lab.  We talked about the DBA role and the shared responsibility model, about new tools used to administer RDS databases in lieu of shell access (like Performance Insights and Enhanced Monitoring), and about how RDS helps implement industry best practices like standardization and automation. On a more technical level, people were interested to learn about the “pgbench” tool provided with postgresql.

In addition to the lab, I also managed to catch part of Simon Riggs’ session Essential PostgreSQL11 Database Administration – in particular, the part about PostgreSQL 11 new features.  One interesting new thing I learned was about some work done specifically around the performance of indexes on monotonically increasing keys.

Interesting Conversations

https://ardentperf.files.wordpress.com/2019/03/img_2736.jpg?w=600&h=450 600w, https://ardentperf.files.wordpress.com/2019/03/img_2736.jpg?w=150&h=113 150w" sizes="(max-width: 300px) 100vw, 300px" />Of course I learned just as much outside of the sessions as I learned in the sessions.  I ended up eating lunch with Alexander Kukushkin who helped facilitate a 3 hour hands-on session today about Understanding and implementing PostgreSQL High Availability with Patroni and enjoyed hearing a bit more about PostgreSQL at Zalando. Talked with a few people from a government organization who were a long-time PostgreSQL shop and interested to hear more about Aurora PostgreSQL. Talked with a guy from a large financial and media company about flashback query, bloat and vacuum, pg_repack, parallel query and partitioning in PostgreSQL.

And of course lots of discussions about the professional community. Met PostgresConf conference volunteers from California to South Africa and talked about how they got involved in the community.  Saw Lloyd and chatted about the Seattle PostgreSQL User Group.

The training and summit days are wrapping up and now it’s time to get ready for the next three days: keynotes, breakout sessions, exposition, a career fair and more!  I can’t wait.  :)

I’ve recently received a number of correspondences regarding one of my most popular blog posts, dating back to February 2008: Index Rebuild vs. Coalesce vs. Shrink Space (Pigs – 3 Different Ones). In the comments section, there’s an interesting discussion where I mention: “If Oracle19 does everything for you and all the various indexes structures get […]

In a previous post I measured the CPU usage when running a database transaction in the same engine (SQL), or two engines in the same process (PL/SQL + SQL or JavaScript + SQL) or two processes (Javascript client + server SQL):

ODC Appreciation Day : Reduce CPU usage by running the business logic in the Oracle Database

For the JavaScript + SQL running in the same process, I used the Oracle Multi-Lingual Engine in beta 0.2.7 but there is now a new beta 0.3.0 and this post runs the same (or similar) with this.

I’ve installed this MLE in a previous post:

Oracle Multi-Lingual Engine

And here is the demo where I run 400000 amount transfers between accounts. Here are the tables:

SQLcl: Release 18.4 Production on Sun Mar 17 15:42:34 2019
Copyright (c) 1982, 2019, Oracle.  All rights reserved.
Last Successful login time: Sun Mar 17 2019 15:42:36 +00:00
Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0_MLE - 64bit Beta

15:42:39 SQL> create table CUSTOMERS (
      CUSTOMER_ID number generated always as identity 
                  constraint CUSTOMER_PK primary key,
      CUSTOMER_NAME varchar2(42)
     );

Table created.

15:42:42 SQL> create table ACCOUNTS (
      ACCOUNT_ID  varchar2(10) constraint ACCOUNT_PK primary key,
      CUSTOMER_ID number,
      AMOUNT      number default 0
     );

Table created.

15:42:46 SQL> insert /*+ append */ into CUSTOMERS (CUSTOMER_NAME)
      select x from (
       select to_char( date'-4712-01-01'+rownum-1,'Jsp') x 
       from xmltable('1 to 1000000')
      ) where length(x)=42 and rownum<=4000;

4000 rows created.

15:42:49 SQL> commit;

Commit complete.

15:42:51 SQL> select * from CUSTOMERS 
              order by CUSTOMER_ID fetch first 10 rows only;

  CUSTOMER_ID CUSTOMER_NAME
  ----------- ------------------------------------------
            1 Three Thousand Three Hundred Seventy-Three
            2 Three Thousand Three Hundred Seventy-Seven
            3 Three Thousand Three Hundred Seventy-Eight
            4 Three Thousand Seven Hundred Seventy-Three
            5 Three Thousand Seven Hundred Seventy-Seven
            6 Three Thousand Seven Hundred Seventy-Eight
            7 Three Thousand Eight Hundred Seventy-Three
            8 Three Thousand Eight Hundred Seventy-Seven
            9 Three Thousand Eight Hundred Seventy-Eight
           10 Seven Thousand Three Hundred Seventy-Three

10 rows selected.

15:42:54 SQL> insert /*+ append */ into ACCOUNTS                   
              (ACCOUNT_ID,CUSTOMER_ID,AMOUNT)
      select 'X'||to_char(rownum,'FM0999999'),CUSTOMER_ID,10000 
      from CUSTOMERS cross join xmltable('1 to 100')
     ;

400000 rows created.

15:42:57 SQL> commit;

Commit complete.

15:42:58 SQL> commit;

Commit complete.

15:43:15 SQL> select * from ACCOUNTS 
              order by ACCOUNT_ID fetch first 10 rows only;

ACCOUNT_ID     CUSTOMER_ID   AMOUNT
----------     -----------   ------
X0000001              1150    10000
X0000002              1151    10000
X0000003              1152    10000
X0000004              1153    10000
X0000005              1154    10000
X0000006              1155    10000
X0000007              1156    10000
X0000008              1157    10000
X0000009              1158    10000
X0000010              1159    10000

10 rows selected.

15:43:16 SQL> select /*+ full(ACCOUNTS) cache(ACCOUNTS) */ 
              count(*),avg(amount) from ACCOUNTS;

  COUNT(*)   AVG(AMOUNT)
  --------   -----------
    400000         10000

I have a ‘show-cpu-seconds-from-ps.sh’ script that displays the cputime delta from ps output.

Here I run all in one SQL statement: 5 seconds of CPU

15:44:23 SQL> set timing on
15:44:28 SQL> host sh /tmp/sqlcl/show-cpu-seconds-from-ps.sh init to reset cputime counter

15:44:30 SQL> update ACCOUNTS set AMOUNT=
  2          case
  3           when ACCOUNT_ID='X0000001' then AMOUNT+(select 1*count(*) from ACCOUNTS where ACCOUNT_ID<>'X0000001')
  4           else AMOUNT-1
  5          end
  6  /

400000 rows updated.

Elapsed: 00:00:04.451
15:44:43 SQL> host sh /tmp/sqlcl/show-cpu-seconds-from-ps.sh diff to show the delta cputime
         5 cpu seconds in pid=     19971 oracleCDB1 (LOCAL=NO)

15:44:43 SQL> select * from ACCOUNTS order by ACCOUNT_ID fetch first 10 rows only;
ACCOUNT_ID     CUSTOMER_ID   AMOUNT
X0000001              1150   409999
X0000002              1151     9999
X0000003              1152     9999
X0000004              1153     9999
X0000005              1154     9999
X0000006              1155     9999
X0000007              1156     9999
X0000008              1157     9999
X0000009              1158     9999
X0000010              1159     9999

10 rows selected.

Elapsed: 00:00:00.019
15:44:43 SQL> rollback;

Rollback complete.

Elapsed: 00:00:04.158

This is the actual CPU cycles needed to update those 400000 account amounts: 5 seconds. And the rollback is the same.

Now with a PL/SQL procedure: 30 seconds of CPU (because of the context switches between the PL/SQL and SQL engines)

15:44:47 SQL> create or replace procedure transfer(acc1 varchar2, acc2 varchar2, amount number) as
  2  begin
  3   -- debit acc1
  4   update ACCOUNTS set ACCOUNTS.AMOUNT = ACCOUNTS.AMOUNT - transfer.amount where ACCOUNT_ID=acc1;
  5   if sql%rowcount <> 1 then raise_application_error(-20000,'Account '''||acc1||''' unknown'); end if;
  6   -- credit acc2
  7   update ACCOUNTS set ACCOUNTS.AMOUNT = ACCOUNTS.AMOUNT + transfer.amount where ACCOUNT_ID=acc2;
  8   if sql%rowcount <> 1 then raise_application_error(-20000,'Account '''||acc2||''' unknown'); end if;
  9  end;
 10  /

Procedure created.
Elapsed: 00:00:00.113
15:46:11 SQL> desc transfer

PROCEDURE transfer
Argument Name   Type       In/Out   Default?
ACC1            VARCHAR2   IN
ACC2            VARCHAR2   IN
AMOUNT          NUMBER     IN

15:46:38 SQL> set timing on
15:46:41 SQL> host sh /tmp/sqlcl/show-cpu-seconds-from-ps.sh init to reset cputime counter

15:46:43 SQL> exec for c in (select * from ACCOUNTS where ACCOUNT_ID<>'X0000001') loop transfer(c.ACCOUNT_ID,'X0000001',1); end
 loop;

PL/SQL procedure successfully completed.

Elapsed: 00:00:30.283
15:47:15 SQL> host sh /tmp/sqlcl/show-cpu-seconds-from-ps.sh diff to show the delta cputime
        30 cpu seconds in pid=     19971 oracleCDB1 (LOCAL=NO)

15:47:38 SQL> select * from ACCOUNTS order by ACCOUNT_ID fetch first 10 rows only;
ACCOUNT_ID     CUSTOMER_ID   AMOUNT
X0000001              1150   409999
X0000002              1151     9999
X0000003              1152     9999
X0000004              1153     9999
X0000005              1154     9999
X0000006              1155     9999
X0000007              1156     9999
X0000008              1157     9999
X0000009              1158     9999
X0000010              1159     9999

10 rows selected.

Elapsed: 00:00:00.015
15:47:43 SQL> rollback;

Rollback complete.

Elapsed: 00:00:04.266

Now with a JavaScript client: 157 seconds of CPU (in the same database session process, but two engines).

15:48:38 SQL> disconnect

Disconnected from Oracle Database 12c Enterprise Edition Release 12.2.0.1.0_MLE - 64bit Beta
15:48:54 SQL> script
  2  var DriverManager = Java.type("java.sql.DriverManager");
  3  if ( ! con === undefined ) { con.rollback(); con.close(); }
  4  var con = DriverManager.getConnection("jdbc:oracle:thin:@//localhost/PDB1","demo","demo");
  5  con.setAutoCommit(false);
  6  var sql = con.createStatement();
  7  .

15:49:10 SQL> save script01-init.js replace
Wrote file script01-init.js
15:49:16 SQL> @    script01-init.js
Elapsed: 00:00:01.019
15:49:18 SQL> script
  2  print("First 10 accounts:");
  3  var res=sql.executeQuery(" select ACCOUNT_ID,AMOUNT from ACCOUNTS order by 1 fetch first 10 rows only");
  4  while(res.next()){print(" ACCOUNT_ID: "+res.getString(1)+" "+"AMOUNT: "+res.getString(2)); }
  5  .

15:49:33 SQL> save script02-query.js replace
Wrote file script02-query.js
15:49:35 SQL> @    script02-query.js
First 10 accounts:
 ACCOUNT_ID: X0000001 AMOUNT: 10000
 ACCOUNT_ID: X0000002 AMOUNT: 10000
 ACCOUNT_ID: X0000003 AMOUNT: 10000
 ACCOUNT_ID: X0000004 AMOUNT: 10000
 ACCOUNT_ID: X0000005 AMOUNT: 10000
 ACCOUNT_ID: X0000006 AMOUNT: 10000
 ACCOUNT_ID: X0000007 AMOUNT: 10000
 ACCOUNT_ID: X0000008 AMOUNT: 10000
 ACCOUNT_ID: X0000009 AMOUNT: 10000
 ACCOUNT_ID: X0000010 AMOUNT: 10000
Elapsed: 00:00:00.181
15:49:37 SQL> script
  2  var pre1=con.prepareStatement(" update ACCOUNTS set AMOUNT=AMOUNT-? where ACCOUNT_ID=?");
  3  var pre2=con.prepareStatement(" update ACCOUNTS set AMOUNT=AMOUNT+? where ACCOUNT_ID=?");
  4  function transfer (acc1,acc2,amount) {
  5   pre1.setInt(1,amount); pre1.setString(2,acc1); pre1.execute();
  6   pre2.setInt(1,amount); pre2.setString(2,acc2); pre2.execute();
  7  }
  8  var res=sql.executeQuery(" select ACCOUNT_ID from ACCOUNTS where ACCOUNT_ID<>'X0000001'");
  9  print("Calling transaction for each account...");var t0=new Date();var cnt=0;
 10  while(res.next()){ transfer(res.getString(1),'X0000001',1); cnt++ }
 11  print(cnt+" transactions executed in "+(new Date() - t0)/1000+" seconds");
 12  .

15:50:17 SQL> save script02-run.js replace
Wrote file script02-run.js
15:50:18 SQL> set timing on
15:50:22 SQL> host sh /tmp/sqlcl/show-cpu-seconds-from-ps.sh init to reset cputime counter

15:50:25 SQL> @    script02-run.js
Calling transaction for each account...
399999 transactions executed in 138.016 seconds
Elapsed: 00:02:18.082
15:52:45 SQL> host sh /tmp/sqlcl/show-cpu-seconds-from-ps.sh diff to show the delta cputime
        52 cpu seconds in pid=     19945 /opt/oracle/product/12.2.0.1/dbhome_1/jdk/jre/bin/java -Djava.awt.headless=true -Dappl
e.awt.UIElement=true -Xss10M -client
       105 cpu seconds in pid=     20426 oracleCDB1 (LOCAL=NO)

15:52:56 SQL> @    script02-query.js
First 10 accounts:
 ACCOUNT_ID: X0000001 AMOUNT: 409999
 ACCOUNT_ID: X0000002 AMOUNT: 9999
 ACCOUNT_ID: X0000003 AMOUNT: 9999
 ACCOUNT_ID: X0000004 AMOUNT: 9999
 ACCOUNT_ID: X0000005 AMOUNT: 9999
 ACCOUNT_ID: X0000006 AMOUNT: 9999
 ACCOUNT_ID: X0000007 AMOUNT: 9999
 ACCOUNT_ID: X0000008 AMOUNT: 9999
 ACCOUNT_ID: X0000009 AMOUNT: 9999
 ACCOUNT_ID: X0000010 AMOUNT: 9999
Elapsed: 00:00:00.015
15:53:13 SQL> script
  2  con.rollback();
  3  con.close();
  4  .

15:53:20 SQL> save script02-close.js replace
Wrote file script02-close.js
15:53:22 SQL> @    script02-close.js
Elapsed: 00:00:06.198

And finally running JavaScript in the MLE engine: 223 seconds of CPU. This MLE, in beta, may not be fully optimized, so the time is not very relevant. The point is that the whole is running 100% in the same process.

15:53:31 SQL> connect demo/demo@//localhost/pdb1
Connected.

15:55:34 SQL> create or replace javascript source named "demo.js" as
  2  function transfer (acc1,acc2,amount) {
  3   var sql = _dbRequire('@oracle/sql');
  4   sql.execute(" update ACCOUNTS set AMOUNT=AMOUNT-:amount where ACCOUNT_ID=:acc1",[amount,acc1]);
  5   sql.execute(" update ACCOUNTS set AMOUNT=AMOUNT+:amount where ACCOUNT_ID=:acc2",[amount,acc2]);
  6  }
  7  module.exports.run = function () {
  8   var sql = _dbRequire('@oracle/sql');
  9   var res=sql.execute(" select ACCOUNT_ID from ACCOUNTS where ACCOUNT_ID<>'X0000001'");
 10   for (var row of res.rows) {
 11    transfer(row[0],'X0000001',1);
 12   }
 13  }
 14  /

Function created.
Elapsed: 00:00:00.013
15:56:02 SQL> create or replace procedure run as language javascript
  2  name 'demo\.js.run()';
  3  /

Procedure created.
Elapsed: 00:00:00.032
15:56:14 SQL> select * FROM user_libraries;

no rows selected
Elapsed: 00:00:00.122
15:56:19 SQL> select object_name,procedure_name,object_type from user_procedures;
OBJECT_NAME   PROCEDURE_NAME   OBJECT_TYPE
RUN                            PROCEDURE
TRANSFER                       PROCEDURE

Elapsed: 00:00:00.291
15:56:21 SQL> select object_name,procedure_name,object_type from user_procedures;
OBJECT_NAME   PROCEDURE_NAME   OBJECT_TYPE
RUN                            PROCEDURE
TRANSFER                       PROCEDURE

Elapsed: 00:00:00.012
15:56:36 SQL> set timing on
15:56:51 SQL> host sh /tmp/sqlcl/show-cpu-seconds-from-ps.sh init to reset cputime counter

15:56:53 SQL> call demo.run();

Call completed.

Elapsed: 00:03:32.463
16:00:28 SQL> host sh /tmp/sqlcl/show-cpu-seconds-from-ps.sh diff to show the delta cputime
       223 cpu seconds in pid=     20761 oracleCDB1 (LOCAL=NO)

The important point with this MLE engine is that you can write your code without being tied to a platform. You write code (or use libraries of code, copy/paste from StackOverflow…) in the latest trendy languages (JavaScript and Python for the moment, whatever in the future). And it can run on the client, the application server, or in the database. Then, the best colocation of code can be achieved without duplicating the logic into different languages. In summary, the developer thinks “serverless” for simplicity and agility and the operations run “full server” for efficiency and scalability.

But that’s for the future. Follow the MLE and be involved in the community:

Space: Multilingual Engine | Oracle Community

For your curiosity, where is the perf-top for the last run in MLE showing the work in oracle and in libmle.so engines:

Here is a script I use a lot especially when importing a schema with Data Pump and checking for invalid objects. I usually don’t care about compilation errors at compile time but just run UTL_RECOMP.RECOMP_PARALLEL at the end and check for errors on invalid objects. Here is an example.

I have imported a schema with Data pump and got some compilation errors:

I want to resolve them, or at least to understand them.

If I query DBA_ERRORS, I get the following:

This is a small example, but it can be huge. Not very helpful:

• I have some error messages like “PL/SQL: ORA-00942: table or view does not exist” but with no mention of wich table. I have to go to the source with line and position.
• I have some other errors which mention an object which is invalid, but the reason may be a consequence of the previous one. Then I want to see only the previous one.

This is why I use the following query to filter only top-level errors, lokking at DBA_DEPENDENCY to get the first ones, and show the line from DBA_SOURCE in order to give a better idea.

Here is my output for the same errors:

I can see clearly that I have only one object in error, which has a SELECT statement ignored because the table ELEMENT_INFO is not visible. No need to dig into the code, just checking why this table is not there.

Here is the script, just mention the schema name instead of ‘%’:

with 
 schemas as (select username owner from dba_users where 
 username like '%'
),
errors as (
 select * from dba_errors natural join schemas
),
top_errors as (
 -- only top errors in dependency
 select * from errors
 where (owner,name,type) not in (
  select owner,name,type 
  from dba_dependencies 
   where (referenced_owner,referenced_name,referenced_type) 
   in (select owner,name,type from errors)
  )
 )
-- here is the select to join with dba_source
select /*+ first_rows(1) */ decode(n,-1,'* ','  ')||text text from (
 -- name/type of the object in error
 select
 distinct -1       n,owner,name,type,line
 ,type||' '||owner||'.'||name||' line '||line text
 from top_errors
 union all
 -- line with error (from dba source)
 select  0       n,owner,name,type,line,text
 from dba_source where (owner,name,type,line)
  in ( select owner,name,type,line from top_errors)
 union all
 -- error message with indication of the position in the line
 select sequence n,owner,name,type,line
 ,lpad(' ',position-1,' ')||'^'||text text
 from top_errors 
) order by owner,name,type,line,n;

I’ll be happy to have your feedback on Twitter: https://twitter.com/FranckPachot/status/1106246663096713222