Isolation Levels

Read Committed

Read committed is the weakest named level in the toy matrix.

highlighted = computed this step

Read committed

Read committed is the weakest named level in this toy matrix. The point is set membership, not product behavior.

read committed row\text{read committed row}

One blocked label

The read committed row blocks 1 anomaly label and allows 3 labels in this pinned matrix.

blocked=1,allowed=3\text{blocked}=1,\quad \text{allowed}=3

isolation levels are rendered as a tiny pedagogical matrix over named anomalies only; ANSI completeness, vendor behavior, performance, and operational guarantees are out of scope.

Read committedleveldirty_readnon_repeatable_readlost_updatewrite_skewread_committedblockedallowedallowedallowedrepeatable_readblockedblockedallowedallowedsnapshot_isolationblockedblockedblockedallowedserializableblockedblockedblockedblocked blocked versus allowedlevelblockedCountblockedallowedCountallowedread_committed1dirty_read3non_repeatable_read, lost_update, write_skewrepeatable_read2dirty_read, non_repeatable_read2lost_update, write_skewsnapshot_isolation3dirty_read, non_repeatable_read, lost_update1write_skewserializable4dirty_read, non_repeatable_read, lost_update, write_skew0none stronger-than cover edgesstrongerweakerrepeatable_readread_committedsnapshot_isolationrepeatable_readserializablesnapshot_isolation

Summary

The row is a small exact fact table. Note: it does not describe every behavior of any real read committed implementation.

one row is one modeled fact set\text{one row is one modeled fact set}