TempDB

tempdb is the whole instance's shared scratch database: temporary tables, sorts, hash joins, the version store. Because everyone shares it, it quickly becomes a bottleneck.

What is monitored

• Usage – how much space user objects, internal objects and the version store consume.
• Contention – waits on allocation pages (PFS/GAM/SGAM). High contention shows up as PAGELATCH waits and slows down every session using tempdb.

Typical remedies

• Multiple equally sized tempdb data files (spreads the allocation load).
• Tame queries that sort/spill excessively.

tempdb contention often first appears in wait statistics as PAGELATCH_* – this page shows the corresponding cause.