Storage Model

N-ary Storage Model (Row/Record)

Concurrency Control

Multi-version Concurrency Control (MVCC) Two-Phase Locking (Deadlock Prevention) Two-Phase Locking (Deadlock Detection)

Sybase ASE uses multi-version concurrency control where all transactions are performed in the in-memory row storage or on disk MVCC, which enables the server to lock rows for writing in one session while granting access to unaltered rows in another session. ASE supports locking at table, page, and row level by providing allpages locking, datapages locking, and datarows locking.

Locking Schemes:

• Allpages locking locks data pages and index pages
• Datapages locking locks only data pages
• Datarows locking locks only data rows

For each scheme, ASE can acquire a table lock for the entire table or can acquire page and row locks to lock only the affected pages or rows. The types of page and row locks include shared locks for read operations, exclusive locks for inserts, deletes, and updates, and update locks during the initial phases of an update, delete, or fetch. Update locks can be promoted to exclusive locks immediately after no other shared locks exist on the page or row.

Isolation Levels

Read Uncommitted Read Committed Serializable Repeatable Read

ASE provides four isolation levels:

• Isolation level 0 - This level is also known as read uncommitted or dirty read. It allows a task to read uncommitted changes.
• Isolation level 1 - This is the default level. It is also known as read committed and prevents dirty reads. Queries at this level can read only committed changes.
• Isolation level 2 - This level prevents non-repeatable reads.
• Isolation level 3 - This level prevents phantoms.

Compression

Naïve (Page-Level) Naïve (Record-Level)

ASE provides row-level and page-level compression. Row-level compression is for fixed-length regular data. Some fixed-length data types, such as tiny integer (which uses 1 byte), cannot be compressed. Page-level compression compresses redundant data on a page. A compressed ASE database can include both compressed and uncompressed tables or partitions.

Hardware Acceleration

RDMA

ASE uses the Virtual Server Architecture to take advantage of the parallel processing done by symmetric multiprocessing systems. ASE can be run as a single process, a single multi-threaded process, or multiple cooperating processes. The ASE Cluster Edition 16sp01 supports RDMA.

Foreign Keys

Supported

ASE supports foreign key constraints. When a foreign key is created on a table, an index for the key is automatically created.

Stored Procedures

Supported

Storage Architecture

In-Memory

The database runs entirely in the Adaptive Server memory space (cache), so neither log nor data is ever written to disk, and I/O is not required. Its performance can be better than a disk-oriented database, at the cost of durability. In the event of memory failure, the database cannot be recovered.

Checkpoints

Fuzzy

ASE takes checkpoints automatically based on recovery interval requirement and also supports manual checkpoints.

Indexes

Bw-Tree

ASE uses B tree indexing, and indexes provided are clustered or non-clustered. Only one clustered index can be created on a table, but up to 249 non-clustered indexes can be created per table. Index entries are stored as rows on index pages and contain key and value pointers to lower levels of the index, data pages, or individual data rows. An index on a 15-byte field has around 100 rows per index page. If a table is partitioned, local and global indexes can be created.

Index Types:

• Clustered indexes - Table data is stored in index key order. For allpages-locked tables, rows are stored in key order on pages that are linked in key order. For data-only-locked tables, indexes are used to handle data storage on rows and pages, but key ordering is not preserved.
• Non-Clustered indexes - Storage order of data is unrelated to index keys.
• Local indexes - Local indexes are index subtrees that index only one data partition.
• Global indexes - Global indexes span all data partitions in a table.

Query Interface

SQL

Data Model

Relational

Sybase ASE is a relational database and handles normalized data models for OLTP workloads well. It also supports star and snowflake models for OLAP workloads.

Joins

Nested Loop Join Hash Join Sort-Merge Join

Sybase ASE provides four main joins: NESTED LOOP JOIN, MERGE JOIN, HASH JOIN, and NARY NESTED LOOP JOIN (a variant of nested loop join). Nested loop join works well with relatively small data sets, merge join works well for moderately sized data sets, and hash join performs well for large datasets. Hash joins parallelize and scale better than other joins and maximize throughput in data warehouses well.