The primary technical distinction between 32-bit and 64-bit database systems lies in memory addressing capabilities. A 32-bit database can directly address up to 4GB of RAM (typically 2-3GB usable due to OS limitations), while 64-bit systems can theoretically address 16 exabytes (though practical limits are much lower).

For PostgreSQL 9.0+, consider this memory configuration example:
sql
-- 64-bit PostgreSQL configuration (postgresql.conf)
shared_buffers = 8GB -- Recommended: 25% of available RAM
work_mem = 256MB -- For complex sorts/aggregations
maintenance_work_mem = 1GB -- For VACUUM, CREATE INDEX, etc.

Memory-intensive workloads:
- Large in-memory caches (e.g., Microsoft SQL Server Buffer Pool)
- Complex analytical queries with hash joins
- GIS operations with PostGIS extensions

Database size thresholds:
- MySQL with tables >4GB (especially InnoDB)
- SQL Server Columnstore indexes
- PostgreSQL TOAST tables for large objects

A test on MySQL 8.0 showed:
sql
-- 32-bit vs 64-bit throughput comparison
-- Test query (TPC-H benchmark modified)
SELECT l_orderkey, SUM(l_extendedprice*(1-l_discount)) AS revenue
FROM lineitem
WHERE l_shipdate <= DATE_SUB('1998-12-01', INTERVAL 90 DAY) GROUP BY l_orderkey HAVING SUM(l_quantity) > 300;

Results:
- 32-bit: 14.2 seconds (hit 3.2GB memory limit)
- 64-bit: 8.7 seconds (utilized 7.8GB RAM)

For SQL Server, the upgrade path requires attention:
powershell
# Verify current architecture
(Get-ItemProperty "HKLM:\SOFTWARE\Microsoft\Microsoft SQL Server\MSSQL15.MSSQLSERVER\MSSQLServer").CurrentVersion
# Expected output: "15.0.2000.5 (X64)" or similar

- Embedded database applications
- Development/test environments
- Legacy systems with 32-bit dependencies
- Memory-constrained VMs (though consider 64-bit with memory limits)

For these cases, MySQL can be configured conservatively:
ini
# my.cnf for 32-bit systems
[mysqld]
innodb_buffer_pool_size=1G
key_buffer_size=256M
query_cache_size=0 # Disabled for modern versions

The fundamental architectural difference lies in memory addressing. A 32-bit database server can theoretically address up to 4GB of RAM (2³²), though Windows imposes a practical limit of 2-3GB per process. In contrast, 64-bit systems can address 16 exabytes (2⁶⁴), though current implementations typically support 128TB-256TB.

-- PostgreSQL example showing memory configuration
# For 32-bit PostgreSQL (postgresql.conf)
shared_buffers = 1GB      # Typically 25% of available RAM
work_mem = 16MB           # Per-operation memory

# For 64-bit PostgreSQL
shared_buffers = 8GB      # Can utilize more RAM
work_mem = 64MB           # Larger operations possible

Consider 64-bit databases when:

• Working with datasets exceeding 4GB in active memory
• Running complex analytical queries requiring large hash joins
• Using memory-intensive features like PostgreSQL's JIT compilation
• Deploying on servers with >16GB RAM (common in cloud environments)

SQL Server 2008:

The 64-bit version removes the 32-bit AWE memory extension limitations. Columnstore indexes and compression features benefit significantly from 64-bit.

-- SQL Server memory configuration
EXEC sp_configure 'show advanced options', 1;
RECONFIGURE;
EXEC sp_configure 'max server memory (MB)', 24576; -- 24GB for 64-bit
EXEC sp_configure 'min server memory (MB)', 4096;
RECONFIGURE;

MySQL:

64-bit provides better InnoDB buffer pool performance. For large datasets, the difference in throughput can be 30-40%.

# my.cnf configuration
[mysqld]
innodb_buffer_pool_size=12G  # 32-bit max ~2.7G
innodb_log_file_size=2G
key_buffer_size=512M

PostgreSQL 9.0+: