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https://issues.apache.org/jira/browse/DERBY-2798?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12509841
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Bastian Wassermann commented on DERBY-2798:
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I have patched this version of Derby and i cant see any difference to the
unpatched version.
I thought that this Version would run derby out of memory, so there are no
writtings and readings to disk, but when i try this version there is still
access to harddisk (when ever i put something into a table)
I dont know much about how databases work, but with every insert command the
derby db writtes to the log1.dat file in the database folder. Is this logging
an feature, which can be de-activated or is this access a necessary function.
So can this access been switched off, so nothing would be written to hard-disk
or is this impossible.
I thought of a database, that works 100% in virtual memory and writtes the
datas in interval-times to harddisk. Is this possible. If you know some manuals
which would help me in this matter, i would be very thankful.
> A new approach for main-memory database
> ---------------------------------------
>
> Key: DERBY-2798
> URL: https://issues.apache.org/jira/browse/DERBY-2798
> Project: Derby
> Issue Type: New Feature
> Components: Store
> Affects Versions: 10.2.2.0
> Environment: all
> Reporter: Knut Magne Solem
> Attachments: Derby-10.2.2.0-memstore.diff, DERBY-2798-10.3.1.0.diff,
> DERBY-2798-10.3.1.0.stat, DERBY-2798.diff, select.png, update.png
>
>
> As a part of my Masters degree I have created an extension that allows data
> to reside in memory without the need to serialize it to Page-objects. This is
> a pretty big chunk of code and is sort of a proof of concept of another way
> to make an in-memory storage mode.
> I created two new conglomerates, called MemHeap and MemSkiplist. Derby
> interfaces them the same way as it does with Heap and BTree. These new
> conglomerates use RawStore for transaction support and logging, but not for
> storage. Instead it uses a new system service I've called MemStore. This data
> store only stores pointers to Slot-objects organized in arrays corresponding
> to its container/conglomerate/table. A Slot-object consists mainly of a
> DataValueDescriptor[]-object representing a row in a table.
>
> So, instead of just doing dummy-IO in memory where Derby still thinks its
> doing real IO and page caching, this new approach bypasses the cache and
> page-structure by keeping the DataValueDescriptor[]-objects in memory without
> serializing them.
>
> Manipulating operations on data in memory are done via new operation-objects
> (ex. MemInsertOperation, MemInsertUndoOperation, MemDeleteOperation...) with
> still uses RawStore for transaction control and persistence. Checkpointing is
> done by serializing the objects in MemStore fuzzily and completely
> unsynchronized to disk. Recovery consists of de-serializing the objects to
> MemStore before the existing REDO- and UNDO-phase of Derby recovery in
> RawStore will get the data transaction-consistent by replaying or undo the
> new operation-objects in the log.
>
> Locking is hard coded as row based with locking degree SERIALIZABLE.
>
> To get Derby to use the new conglomerates I hacked the SQL-layer to create
> MemHeap-tables and MemSkiplist-indexes when the table name starts with 'mem_'.
>
> Because this is a major rewrite of the access- and storage-layer there is a
> lot of known and unknown bugs and missing functionality. What is working is
> essentially select, insert, update and delete on tables with one primary key.
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