On Mon, Feb 05, 2024 at 05:56:11PM -0600, jltobler wrote: > On 24/02/01 08:52AM, Patrick Steinhardt wrote: > > When finishing a section we will potentially write an index that makes > > it more efficient to look up relevant blocks. The index records written > > will encode, for each block of the indexed section, what the offset of > > that block is as well as the last key of that block. Thus, the reader > > would iterate through the index records to find the first key larger or > > equal to the wanted key and then use the encoded offset to look up the > > desired block. > > > > When there are a lot of blocks to index though we may end up writing > > multiple index blocks, too. To not require a linear search across all > > index blocks we instead end up writing a multi-level index. Instead of > > referring to the block we are after, an index record may point to > > another index block. The reader will then access the highest-level index > > and follow down the chain of index blocks until it hits the sought-after > > block. > > > > It has been observed though that it is impossible to seek ref records of > > the last ref block when using a multi-level index. While the multi-level > > index exists and looks fine for most of the part, the highest-level > > index was missing an index record pointing to the last block of the next > > index. Thus, every additional level made more refs become unseekable at > > the end of the ref section. > > Just to clarify, is only the highest-level index not recording the last > block when multi-level indexes are being used? Or are the indexes at all > levels leaving the last block unreachable? Every level N+1 looses the last block of level N. So the latter. Patrick > > > > The root cause is that we are not flushing the last block of the current > > level once done writing the level. Consequently, it wasn't recorded in > > the blocks that need to be indexed by the next-higher level and thus we > > forgot about it. > > > > Fix this bug by flushing blocks after we have written all index records. > > -Justin
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