Direct INSERTs into HCC tables may be slower since Oracle 12.2

I work with several customers at the moment on their Oracle 12.2/18c “go live” projects. And one of these customers encountered a strange issue when comparing Oracle 11.2.0.4 to Oracle 12.2.0.1/18.3.0: Direct INSERTs into HCC tables may be slower since Oracle 12.2. Actually in this particular case, significantly slower. Read below why this can happen and how the workarounds look like. Hybrid Columnar Compression There’s a lot of material to read and study about Hybrid Columnar Compression (HCC). With HCC we store the same column for a group of rows together. The data block does not store data in row-major…