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https://issues.apache.org/jira/browse/LUCENE-5248?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13783697#comment-13783697
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Shai Erera commented on LUCENE-5248:
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Hmm, maybe the problem is not RUE, but the fact that we don't
commit/reopen/merge means the unused gen'd fieldInfos and DVs files aren't
deleted from the Directory (and it's a RAMDirectory)? This isn't a bug, but can
explain the growth in RAM since RALD references SegInfo which references the
Directory. I'll double-check that later.
About FieldUpdates abstractions, few ideas for very large updates:
* DiskFieldUpdates -- hold the resolved updates on disk, sort on disk and read
from disk, to accommodate very large updates.
* DerefedFieldUpdates -- if there are only few large updates, we can hold
PackedInt for docs (bitsRequired=maxDoc-1), PackedInt for indexes
(bitsRequired=numValues-1) and long[] for values. The values array is much
smaller than the docs array and we use an indexes array to mark for each
document where it takes its value from (in the values array).
I'm sure Adrien will have more (probably better) ideas :).
> Improve the data structure used in ReaderAndLiveDocs to hold the updates
> ------------------------------------------------------------------------
>
> Key: LUCENE-5248
> URL: https://issues.apache.org/jira/browse/LUCENE-5248
> Project: Lucene - Core
> Issue Type: Improvement
> Components: core/index
> Reporter: Shai Erera
> Assignee: Shai Erera
> Attachments: LUCENE-5248.patch, LUCENE-5248.patch
>
>
> Currently ReaderAndLiveDocs holds the updates in two structures:
> +Map<String,Map<Integer,Long>>+
> Holds a mapping from each field, to all docs that were updated and their
> values. This structure is updated when applyDeletes is called, and needs to
> satisfy several requirements:
> # Un-ordered writes: if a field "f" is updated by two terms, termA and termB,
> in that order, and termA affects doc=100 and termB doc=2, then the updates
> are applied in that order, meaning we cannot rely on updates coming in order.
> # Same document may be updated multiple times, either by same term (e.g.
> several calls to IW.updateNDV) or by different terms. Last update wins.
> # Sequential read: when writing the updates to the Directory
> (fieldsConsumer), we iterate on the docs in-order and for each one check if
> it's updated and if not, pull its value from the current DV.
> # A single update may affect several million documents, therefore need to be
> efficient w.r.t. memory consumption.
> +Map<Integer,Map<String,Long>>+
> Holds a mapping from a document, to all the fields that it was updated in and
> the updated value for each field. This is used by IW.commitMergedDeletes to
> apply the updates that came in while the segment was merging. The
> requirements this structure needs to satisfy are:
> # Access in doc order: this is how commitMergedDeletes works.
> # One-pass: we visit a document once (currently) and so if we can, it's
> better if we know all the fields in which it was updated. The updates are
> applied to the merged ReaderAndLiveDocs (where they are stored in the first
> structure mentioned above).
> Comments with proposals will follow next.
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