Tomislav is available for hire
Hire TomislavTomislav Delas
Verified Expert in Engineering
Database Developer
Vinkovci, Croatia
Toptal member since July 16, 2020
Bio
Tomislav is a seasoned IT expert in the software industry dating back to 1996. Most of his expertise is focused on data engineering, including the development of DWH and BI solutions, database and SQL optimization, and database administration. Tomislav has deep knowledge of SQL programming, database administration, Big Data technologies, cloud databases and services across AWS, Azure, and Google Cloud, as well as ETL pipeline development using Python, REST APIs, Informatica, and DataStage.
Portfolio
Kepler Cheuvreux SA
SQL, Oracle, Oracle DBA, Oracle R, Oracle Data Guard, Oracle RMAN, Linux...
Pioneer Works, Inc.
Data Engineering, Spark, Data Build Tool (dbt), Python, Data Modeling...
Kepler Cheuvreux SA
SQL, Oracle, Oracle DBA, Oracle R, Database Administration (DBA), Scripting...
Experience
- Database Architecture - 20 years
- SQL - 20 years
- Data Modeling - 20 years
- ETL - 20 years
- PostgreSQL - 10 years
- Python - 7 years
- Big Data - 4 years
- Pandas - 2 years
Preferred Environment
Amazon Web Services (AWS), Google Cloud Platform (GCP), ETL, Python, Databases, Big Data, SQL, Data Engineering, Data Warehousing, Informatica
The most amazing...
...thing I've built with a core team was a telecom company's first in-house data warehouse 30 years ago, along with their first big data environment later.
Work Experience
Senior Oracle DBA (via Toptal)
2026 - 2026
Kepler Cheuvreux SA
- Conducted health checks on Oracle production databases in a standby Data Guard configuration, recommending optimizations with a focus on storage management.
- Configured Oracle log listener file retention policies, specifically using adrci and listener.ora.
- Moved production tables to archive tablespaces and resized datafiles and undo tablespaces.
- Analyzed RMAN backups, optimized backup storage, and fixed RMAN backup scripts.
Technologies: SQL, Oracle, Oracle DBA, Oracle R, Oracle Data Guard, Oracle RMAN, Linux, Database Administration (DBA)
Data Engineer
2025 - 2026
Pioneer Works, Inc.
- Monitored data pipelines in a data warehouse ecosystem as part of a weekly on-call rotation, covering Airflow DAGs, dbt jobs, AWS Databricks, Redshift, and Spark, and resolved issues by fixing and optimizing code.
- Developed new features by delivering Jira-assigned data engineering tickets, working with Airflow, Python, Databricks (SQL and Python notebooks), Spark, Redshift, and dbt (models, tests, and Jinja scripts).
- Worked as a data engineer and solved many operational tickets (inquiries) from business and data science users, regarding data in the data warehouse and data pipelines.
- Migrated a number of Databricks server compute jobs to serverless compute mode jobs.
Technologies: Data Engineering, Spark, Data Build Tool (dbt), Python, Data Modeling, Spark SQL, Databricks, Data Pipelines, Debezium, Apache Airflow, Redshift, Looker, Amazon S3 (AWS S3), Docker
Senior Oracle Database Administrator
2025 - 2025
Kepler Cheuvreux SA
- Optimized storage usage in Oracle databases by reorganizing datafiles, archiving data, compressing, and recreating large objects (tables and indexes).
- Fixed Oracle backup (RMAN Utility) scripts to support backup, recovery, and standby database operations.
- Synchronized production databases with development databases using Oracle export/import utilities, along with custom SQL and Linux shell scripts (including the sed utility).
- Developed custom shell and SQL scripts for database health monitoring and notifications.
- Audited failed connections to databases that were locking user accounts and resolved the issue.
Technologies: SQL, Oracle, Oracle DBA, Oracle R, Database Administration (DBA), Scripting, Linux, Oracle Backups, Import/Export, Oracle RMAN
Oracle Database Administrator (DBA)
2023 - 2025
SIG Susquehanna
- Optimized the performance of many SQL-driven jobs in the Oracle database.
- Worked on ETL pipelines for Oracle, Big Data (Hive), and Apache Druid.
- Developed many new features for business users' change requests.
- Reorganized big tables and objects, saving storage.
Technologies: Oracle, Oracle PL/SQL, Oracle DBA, Hadoop, Druid.io, Data Engineering, SQL, Apache Airflow, Data Processing, Microsoft Excel, Data, Data Architecture, Oracle 12c, SQL Stored Procedures, Data Integration, Performance Tuning, Database Administration (DBA), SQL Functions, SQL Triggers, Database Replication, Excel 2016, ETL Pipelines, Spark SQL, Data Build Tool (dbt)
BigQuery Specialist
2023 - 2023
ABS Media Limited
- Developed integration for Nexudus and Zapier application systems with Google Big Query.
- Developed DWH layers and models on top of Google Big Query.
- Developed and loaded Google Big Query layer with business rules and transformations, ready for reporting and BI dashboards.
Technologies: Data Engineering, BigQuery, Google BigQuery, APIs, Looker, ETL, Zapier, Data Processing, Microsoft Excel, Data Visualization, Data, Data Architecture, SQL Stored Procedures, Data Integration, Performance Tuning, Database Administration (DBA), Dashboards, Looker Studio, SQL Functions, SQL Triggers, Excel VBA, ETL Pipelines, Data Build Tool (dbt)
Data Engineer
2020 - 2023
BCG - Gamma
- Developed ETL pipelines (Python, Airflow) for feeding churn management and retention campaigns.
- Conducted many data engineering tasks regarding data ingestion, data quality, and data fixes on source and target systems.
- Accomplished MySQL and PostgreSQL DB administration and optimization tasks.
- Configured Docker infrastructure for the solution landscape.
- Onboarded many new team members on the project in the data engineering area and conducted lots of technical workshops.
- Developed SQL pipelines for data management and data fixing procedures.
Technologies: ETL, Data Engineering, Python, Amazon Web Services (AWS), Apache Airflow, Redshift, Snowflake, PostgreSQL, MySQL, Azure, Docker, Oracle, Data Warehousing, Business Intelligence (BI), Database Optimization, Database Architecture, Database Design, PySpark, Oracle 10g, Amazon S3 (AWS S3), Amazon RDS, Data Transformation, Database Development, Data Modeling, ELT, Data Analysis, Data Processing, Microsoft Excel, Customer Data Platform (CDP), Python 3, Data, Data Architecture, PostgreSQL 10, SQL Stored Procedures, Data Integration, Performance Tuning, Database Administration (DBA), SQL Functions, SQL Triggers, Database Replication, ETL Pipelines, Pandas, NumPy, Spark SQL, Data Build Tool (dbt), Databricks
Data Architect
2020 - 2020
Squeem, LLC
- Developed data model on Google BigQuery for marketing analysis of Sales.
- Completed ETL pipelines (Stitch ETL SW) from Shopify, Drip, Netsuite, and Google Analytics to BigQuery developed Datawarehouse model.
- Developed complex Tableau reports for Sale tracking.
- Stored procedures in Google BigQuery for data transformation.
Technologies: Big Data, Data Engineering, Data Lakes, Data Warehousing, ETL, ETL Implementation & Design, Big Data Architecture, Data Warehouse Design, Data Reporting, Data Analytics, Segment.io, Shopify API, Amazon API Gateway, NetSuite, Tableau, Google BigQuery, BigQuery, Business Intelligence (BI), Database Optimization, Google Analytics, Database Architecture, Database Design, Tableau Server, Shopify, Drip Email, Data Transformation, Database Development, Data Modeling, ELT, Data Analysis, Data Processing, Microsoft Excel, Data Visualization, Customer Data Platform (CDP), Data, Data Architecture, SQL Stored Procedures, Data Integration, Performance Tuning, Database Administration (DBA), Dashboards, SQL Functions, SQL Triggers, ETL Pipelines
IT Solution Architect
2018 - 2020
Croatian Telekom
- Launched the 1st real-time data collection from customer-premises or customer-provided equipment (CPE) to Cloudera Big Data services.
- Tuned Informatica PowerCenter ETL for data warehousing, tuning, and optimizing Spark streaming real-time processes for predictive and proactive fault resolution.
- Extended the data warehouse environment to Cloudera Big Data for data archiving and ETL processes on the Spark engine in Cloudera.
Technologies: Apache Spark, Apache Impala, HDFS, Apache Kafka, Apache Flume, Apache Hive, Oracle, Datastage, Informatica, Big Data, Cloudera, Data Warehousing, Database Optimization, Oracle PL/SQL, Database Architecture, Database Design, Oracle SQL, Query Optimization, Oracle Database Architecture, Oracle 10g, Data Transformation, Database Development, Data Modeling, ELT, Data Analysis, Data Processing, Data, Data Architecture, Oracle 12c, SQL Server Integration Services (SSIS), SQL Stored Procedures, Data Integration, Performance Tuning, Database Administration (DBA), Dashboards, Transact-SQL (T-SQL), SQL Functions, Excel 2016, Excel VBA, ETL Pipelines, GraphDB
Head of IT Data Warehousing and Business Intelligence Section
2016 - 2018
Hrvatski Telekom
- Led big data integration into the data warehouse (new data warehouse architecture).
- Took over the development and operations of the mobile stack of the data warehouse environment.
- Tuned IBM DataStage ETL processes and Oracle data warehouse (DWH) databases.
- Developed alert processes on mobile devices using visualization tools (Power BI).
Technologies: Windows, Linux, Datastage, Microsoft Power BI, Informatica PowerCenter, Microsoft, Oracle, Data Warehousing, ETL, Business Intelligence (BI), Database Optimization, Microsoft SQL Server, Oracle PL/SQL, Database Architecture, Database Design, Oracle SQL, Query Optimization, Oracle Database Architecture, Oracle 10g, Data Transformation, Database Development, Data Modeling, ELT, Data Analysis, Data Processing, Data Visualization, Data, Data Architecture, Flume, Oracle 12c, MSAS, SQL Server Integration Services (SSIS), SQL Stored Procedures, Data Integration, Performance Tuning, Database Administration (DBA), Dashboards, Transact-SQL (T-SQL), SQL Functions, Excel 2016, Excel VBA, ETL Pipelines, Databricks, GraphDB, Neo4j
Head of Database Administration, Apps, & Service Support Work Unit in Information Systems Operations
2010 - 2016
Hrvatski Telekom
- Led the development of a web portal for IT operations that monitored and end-to-end (E2E) message communication between OSS/BSS telecom systems.
- Tuned many OLTP operational Oracle databases in the company, which resulted in quicker and smoother applications.
- Served as the core team member of the revenue assurance project and was in charge of interfaces, overall architecture solution, and development of some parts of the solution.
Technologies: Windows, Linux, Informatica, Microsoft, PL/SQL, SQL, PostgreSQL, Oracle, Database Optimization, Microsoft SQL Server, Oracle PL/SQL, Database Architecture, Database Design, Oracle SQL, Query Optimization, Oracle Database Architecture, Oracle 10g, Data Transformation, Database Development, Data Modeling, ELT, Data Analysis, Data Processing, Data Visualization, Data, Data Architecture, Oracle 12c, MSAS, SQL Server Integration Services (SSIS), SQL Stored Procedures, Data Integration, Performance Tuning, Database Administration (DBA), Transact-SQL (T-SQL), SQL Functions, Database Replication, Excel 2016, ETL Pipelines, Neo4j
Head of T-HT IT Business Intelligence (BI) Development and Operations Team
2003 - 2009
Hrvatski Telekom
- Introduced a new data-warehousing solution in the company while also working as a lead solution architect and developer.
- Developed ETL processes and many custom interfaces.
- Made many OLAP cubes (Microsoft Analysis tools), reports (ad-hoc SQL and Microsoft Reporting Services).
Technologies: Windows, Linux, Informatica, Microsoft, PL/SQL, SQL, PostgreSQL, Oracle, Data Warehousing, ETL, Business Intelligence (BI), Database Optimization, Oracle PL/SQL, Database Architecture, Database Design, Oracle SQL, Oracle Database Architecture, Oracle 10g, Database Development, Data Modeling, ELT, Data Analysis, Data Processing, Data, Data Architecture, Oracle 12c, SQL Stored Procedures, Data Integration, Database Administration (DBA), Dashboards, ETL Pipelines
Head of the IT Department in a Regional Telecommunications Center (Vukovar)
1996 - 2000
Hrvatski Telekom
- Developed the 1st company-wide data warehousing environment.
- Led a development-and-operational IT team, handling all IT regional processes and solutions.
- Oversaw and monitored all operational processes in IT.
Technologies: Reporting, Informatica PowerCenter, Linux, Oracle, Database Optimization, Database Design, Oracle SQL, Oracle Database Architecture, Oracle 10g, Data Processing, Oracle 12c, SQL Stored Procedures, Database Administration (DBA)
Experience
Smart Churn Retention Solution
A project charged with developing and deploying DEEP.AI, a B2C personalization tool for up-selling and cross-selling, retention, and debt management software for Boston Consulting Group (BCG), aimed at BCG's clients in the telecommunications and energy sectors.
As a member of an international team and a Toptal member, I participated in the retention stream of DEEP.AI. I was tasked with various data engineering and other tasks: data pipeline, ETL creation, database data modeling, database, and query optimizations, CI/CD deployment, and pipeline orchestration.
As a member of an international team and a Toptal member, I participated in the retention stream of DEEP.AI. I was tasked with various data engineering and other tasks: data pipeline, ETL creation, database data modeling, database, and query optimizations, CI/CD deployment, and pipeline orchestration.
Customer Data Platform Project on Cloud Warehouse Database
I created the solution and also developed the customer data platform for a Squeem company and brand (as a Toptal client), running an eCommerce business.
My Project Tasks:
• Analyzed Cloud ETL tools for data pipelines (Skyvia, Stitch, Hevo, and so on) as well as cloud data warehouse solutions (Google Big Query, Snowflake, Amazon Redshift, etc.) in the selection process.
• Implemented the creation of data pipelines (ETL) with Stitch Cloud ETL from source applications (Shopify, Drip, Oracle NetSuite, Google Ads, Google Analytics, and Facebook Ads) to Cloud Google BigQuery Data Lake and Data Warehouse.
• Transformed data on BigQuery (SQL and ETL procedures).
• Visualized with Tableau on top of BigQuery datasets.
• Handled data enrichment with segment software (events and personas).
My Project Tasks:
• Analyzed Cloud ETL tools for data pipelines (Skyvia, Stitch, Hevo, and so on) as well as cloud data warehouse solutions (Google Big Query, Snowflake, Amazon Redshift, etc.) in the selection process.
• Implemented the creation of data pipelines (ETL) with Stitch Cloud ETL from source applications (Shopify, Drip, Oracle NetSuite, Google Ads, Google Analytics, and Facebook Ads) to Cloud Google BigQuery Data Lake and Data Warehouse.
• Transformed data on BigQuery (SQL and ETL procedures).
• Visualized with Tableau on top of BigQuery datasets.
• Handled data enrichment with segment software (events and personas).
Data Warehousing Project with Big Data
I developed a new generation of data warehousing in the telecom business incorporating a big data lake using Cloudera services (HDFS, Hive, Impala, and Spark) for extract-transform-load (ETL) using Spark, utilizing the power of big data infrastructure.
Revenue Assurance Project
I built a revenue assurance solution for a telco business. I was the main IT solution architect and developer of some parts of a solution, and I developed interfaces between different systems and monitoring processes.
Proactive Care
A real-time data-driven project that collects data from a DSL customer equipment (CPE) and ingests to big data (usage of Kafka, Flume, Hive, Spark, and Oozie).
I was a core team developer on this project and was charged with interfaces and solution tuning. The project was used for proactive fault repair in the telco company and integrated into OSS daily processes.
I was a core team developer on this project and was charged with interfaces and solution tuning. The project was used for proactive fault repair in the telco company and integrated into OSS daily processes.
Data Warehousing Solution for a Big Telco Provider
I handled the architecture, solution, development, and operation of a DWH solution for a Telco provider. I was responsible for relational databases (Oracle DBA), ETL processes (Informatica and PL/SQL), data quality, reporting (Microsoft tools and Power BI), etc.
Data Warehousing Solution (for Mobile Services) in a Big Telco provider
I handled the architecture, solution, development, and operation of a DWH solution for a Telco provider. I was responsible for relational databases (Oracle DBA), ETL processes (IBM DataStage and PL/SQL), data quality, reporting (IBM tools and Power BI), etc.
Google Big Query Integrations and Reporting
I developed Nexudus and Zapier integrations with Google BigQuery. I also developed a DWH logical and physical model on top of GBQ, with entities prepared and loaded for reporting and BI dashboards for a media business.
Data Warehouse ETL and SQL Optimization
I optimized ETL pipelines built in IBM DataStage and on top of an Oracle database for a large European telco provider. I also reviewed and aligned the DWH solution with the statement of compliance on the Oracle tier, while refactoring PL/SQL code and IBM DataStage jobs for better performance.
Data Reporting Layer on Top of MS SQL Database
I developed an ETL pipeline in the MS T-SQL language, building a data flow from source systems on MS-SQL DB to the target database also on MS-SQL. Within data transformation, I developed a parsing of complex JSON structures and stored them into key and value target structures.
Education
2001 - 2003
Master's Degree in Computer Science
University of Zagreb - Zagreb, Croatia
1990 - 1995
Engineer's Degree in Electrotechnics
University of Zagreb - Zagreb, Croatia
Certifications
DECEMBER 2021 - DECEMBER 2024
AWS Certified Cloud Practitioner
Amazon Web Services
JUNE 2020 - PRESENT
Training: Spark and Python for Big Data with PySpark
Udemy
JUNE 2020 - PRESENT
Training: Informatica Cloud Data Integration
Udemy
NOVEMBER 2019 - PRESENT
Training: Apache Spark
Croz d.o.o. Croatia
SEPTEMBER 2019 - PRESENT
Training: Apache Kafka Security
Udemy
SEPTEMBER 2019 - PRESENT
Training: Apache Kafka Series — Kafka Security
Udemy
AUGUST 2016 - PRESENT
Training: IBM DataStage Development
Poslovna Inteligencija d.o.o. Zagreb
APRIL 2009 - PRESENT
Training: Microsoft Reporting and Analysis Services
Croatian Telekom (Internal)
APRIL 2008 - PRESENT
Training: PowerCenter 8.5 New Features for Administrator Training
Informatica
OCTOBER 2007 - PRESENT
Training: PowerCenter 8 Developer Training
Informatica
MARCH 2007 - PRESENT
Training: Cost-based Optimization, Indexing Strategies, and Explain Plans
Oracle
JUNE 2006 - PRESENT
Oracle Certified Professional
Oracle
APRIL 2006 - PRESENT
Training: ITIL Foundation for IT Service Management
HP Education Services
MARCH 2006 - PRESENT
Training: 6 Sigma — Project Management Advanced
Next Level Consulting
MARCH 2006 - PRESENT
Training : 6 Sigma — Project Management Leadership
Next Level Consulting
FEBRUARY 2006 - PRESENT
Training: 6 Sigma — Project Management Basics
Next Level Consulting
OCTOBER 2003 - PRESENT
Training: Executive Management Qualifier
Graduate School of Business Administration Zurich
JUNE 2002 - PRESENT
Training: General Management Qualifier
Graduate School of Business Administration Zurich
OCTOBER 1997 - PRESENT
Training: Oracle SQL and PL/SQL
Oracle
Skills
Libraries/APIs
Segment.io, PySpark, Pandas, NumPy, Shopify API
Tools
IBM InfoSphere (DataStage), Microsoft Report Builder, Cloudera, Oozie, Impala, Flume, Informatica PowerCenter, Tableau, Informatica ETL, BigQuery, Stitch Data, Apache Impala, Microsoft Excel, Excel 2016, Microsoft Power BI, Apache Airflow, Google Analytics, Zapier, Spark SQL, Ansible, Looker, Shell
Languages
SQL, Python, Stored Procedure, Transact-SQL (T-SQL), Python 3, Snowflake, Excel VBA
Frameworks
Hadoop, Apache Spark, Spark
Paradigms
ETL, Business Intelligence (BI), ETL Implementation & Design, Database Design, Oracle Database Architecture, Database Development, Management, ITIL
Platforms
Apache Kafka, Linux, Oracle, Windows, Google Cloud Platform (GCP), Amazon Web Services (AWS), Amazon EC2, Azure, Databricks, Microsoft, Shopify, Docker, Debezium
Storage
Oracle Database Tuning, Oracle PL/SQL, Database Architecture, Oracle DBA, Apache Hive, Data Lakes, Database Modeling, Databases, SQL Stored Procedures, Oracle SQL, Oracle 12c, PostgreSQL, PL/SQL, Datastage, Google Cloud SQL, HDFS, PostgreSQL 10, Data Pipelines, Oracle 10g, Amazon S3 (AWS S3), Data Integration, Database Administration (DBA), SQL Functions, SQL Triggers, Database Replication, SQL Server Integration Services (SSIS), MySQL, Microsoft SQL Server, Neo4j, Oracle Cloud, SQL Server Reporting Services (SSRS), Relational Databases, Redshift, Druid.io, JSON
Industry Expertise
Project Management
Other
ETL Development, Big Data, Informatica, MSAS, Data Engineering, Scripting, Data Warehousing, Big Data Architecture, Data Reporting, Database Optimization, Query Optimization, Google BigQuery, Reporting, Informatica Cloud, Segment, ETL Tools, Drip Email, Data Modeling, Data Architecture, Data, Data Warehouse Design, Data Analytics, Amazon RDS, Data Transformation, Message Queues, APIs, Customer Data Platform (CDP), ELT, Data Analysis, Data Processing, Data Visualization, Performance Tuning, Dashboards, ETL Pipelines, Data Build Tool (dbt), Tableau Server, Administration, Looker Studio, GraphDB, eCommerce, Apache Flume, NetSuite, CI/CD Pipelines, Amazon API Gateway, Oracle R, Oracle Backups, Import/Export, Shell Scripting, Optimization, Oracle Data Guard, Oracle RMAN
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