Concurrent read and write access of LargeObject via getBlob() can raise exception

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От Balázs Zsoldos
Тема Concurrent read and write access of LargeObject via getBlob() can raise exception
Дата
Msg-id CAHEBw=Sn5YLE=yNa9HTuFJzcnKojtYK1AO4VxA9D2-nd044amg@mail.gmail.com
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Ответы Re: Concurrent read and write access of LargeObject via getBlob() can raise exception
Список pgsql-jdbc
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Hi,

I created a table with the following fields:
  • blob_id: bigint / primary key, auto increment
  • blob: oid / a pointer to a large object
I created a trigger that unlinks the largeobject if a record is deleted from this table.

If I
  • select a record from my table and get the ResultSet instance
  • parallel, I delete the blob within another transaction
  • call resultSet.getBlob(1).getBinaryStream();
I get the following exception:

Caused by: org.postgresql.util.PSQLException: ERROR: large object 97664 does not exist
        at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2270)
        at org.postgresql.core.v3.QueryExecutorImpl.receiveFastpathResult(QueryExecutorImpl.java:672)
        at org.postgresql.core.v3.QueryExecutorImpl.fastpathCall(QueryExecutorImpl.java:501)
        at org.postgresql.fastpath.Fastpath.fastpath(Fastpath.java:109)
        at org.postgresql.fastpath.Fastpath.fastpath(Fastpath.java:156)
        at org.postgresql.fastpath.Fastpath.getInteger(Fastpath.java:168)
        at org.postgresql.largeobject.LargeObject.<init>(LargeObject.java:106)
        at org.postgresql.largeobject.LargeObject.<init>(LargeObject.java:123)
        at org.postgresql.largeobject.LargeObject.copy(LargeObject.java:128)
        at org.postgresql.jdbc4.AbstractJdbc4Blob.getBinaryStream(AbstractJdbc4Blob.java:26)
        at org.everit.blobstore.jdbc.internal.StreamBlobChannel.read(StreamBlobChannel.java:97)
        at org.everit.blobstore.jdbc.internal.JdbcBlobReader.read(JdbcBlobReader.java:128)

For me that means that it is impossible to be sure that between getting a record from my table and getting the actual content of the blob, the content will be still the same as when I selected the blob record.

I guess I can use safely the table only if I select the record with FOR SHARE.

Regards,
Balázs Zsoldos

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