Hibernate caching and database consistency
I have a question about hibernation caching.
I realized that Hibernate caching is used to avoid hitting the database frequently. Therefore, we use the Hibernate caching mechanism to improve performance.
If a new record is added to the database, when using caching, if we don't get into the database, how will the new added record be added?
Is caching still picking the old entry? can someone explain to me how it works?
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Each concurrency cache strategy has an associated cache synchronization mechanism :
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NONSTRICT_READ_WRITE is a read through cache because objects are stored in the cache when they are fetched from the database (not when they are persisted). Updating an object invalidates the entry in the object's cache.
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READ_WRITE is an asynchronous write through a caching strategy, since the database and cache are not updated transactionally. Soft locks are used to ensure consistency.
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TRANSACTIONAL is a synchronous cache strategy, and how the database and cache are updated atomically.
Hibernation promotes a strong consistency because READ_WRITE and transactional cache coherency is similar to READ_COMMITTED isolation level . Outdated records can be stored in NONSTRICT_READ_WRITE.
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Cache is a component that stores data, so future requests for that data can be served faster; the data stored in the cache can be the result of an earlier computation or duplicates of data stored elsewhere. A cache attack occurs when the requested data can be found in the cache, and a cache miss occurs when it cannot.
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to avoid frequent database hits, we use hibernate caching mechanism to achieve performance.
True.
if a new record was added to the database with caching, if we don't hit the database, how will the new added record be implausible?
We do not get into the database in case of a cache attack , however, if there is a miss cache , the values must be obtained from the database.
At initialization, the cache is empty. Whenever you first access a record, it will not be in the cache. If you access an entry, that entry is checked in the cache first, since the cache is empty. Due to a cache error, the entry will be fetched from the database. The record retrieved from the database is put into the cache, so that the next time the cache is accessed, the writes take place and the database is not accessed.
Please note that there is a limit to how much data / records can be stored in the cache. With limited storage, the cache uses mainly the Least Recent Used algorithm to remove the least recently used or oldest available entries from the cache. Thus, even if you may have previously used the entry, it may happen that it was flushed out of the cache (cache miss). To reload this record, you will need to drop the database. Yes, this record will be added to the database again.
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"If a new record is added to the database, when using caching, if we do not hit the database, how will the new added record be retrieved?"
We ended up in the database for a new entry because it won't be in the cache. It is then stored in the cache and ready to be sent from there in subsequent requests.
"Is caching still picking the old entry?"
If you mean what happens when a row is updated, Hibernate will update the row (disassembled object) in the cache, or discard it (depending on the concurrency cache strategy and cache topology in clustered environments).
However, if the row is updated in the database through another application, unaware of this by Hibernate, then you are correct, the stale data will be served from the cache (until the stale record expires or is flushed out of the cache).
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