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Table types and buffering — transparent, pooled, cluster, and the SAP table buffer

Level: 201 · working knowledge

Status: stub — the settings are here; the worked example is not yet.

One line: A Dictionary table is transparent (one database table), pooled or cluster (several logical tables packed into one physical one — largely gone on HANA), and its technical settings decide whether the application server caches it: a buffered table is read from memory without a database call, and a write from another server makes that memory stale for a while.

The settings that matter

Setting Values Consequence
Table type transparent, pooled, cluster pooled/cluster cannot be joined in Open SQL and are converted to transparent on HANA
Buffering off; single record; generic (by leading key fields); full what is cached per application server
Data class / size category APPL0… storage hints; ignored on HANA
Delivery class A application, C customizing, L temporary… what a client copy and a transport do with the rows
Log data changes on/off writes every change to DBTABLOG (SCU3) — for customizing tables, a compliance requirement

Buffer synchronisation happens between servers every few seconds (rdisp/bufreftime), so a buffered table written on server A can be read stale on server B until then. SELECT … BYPASSING BUFFER reads the database regardless; and several Open SQL forms — joins, aggregates, FOR ALL ENTRIES, DISTINCT — bypass it whether you asked or not.

Why it earns a page

Because "the customizing change did not take effect" on a multi-server system is the buffer, because a large, often-written table with full buffering is a performance bug in the technical settings rather than in any program, and because SE11 → Technical settings is a screen developers change without a transport review. ST10 shows what the buffer is actually doing.

What this page still needs

  • [ ] a snippets/ program showing which SELECT forms bypass the buffer, checked in the SQL trace
  • [ ] ST10 for a buffered table, recorded
  • [ ] delivery class C versus A on a client copy, worked through

See also