TDSWriter.writeReader high memory allocations

[vyaslav]

Driver version

8.4.1

SQL Server version

15

Client Operating System

Ubuntu 20

JAVA/JVM version

11

Table schema

N/A

Problem description

There is alloc of char and byte arrays/buffers on every writeReader invocation:

mssql-jdbc/src/main/java/com/microsoft/sqlserver/jdbc/IOBuffer.java

Line 4099 in 8c0d32b

char[] streamCharBuffer = new char[2 * currentPacketSize];

We use SQLServerBulkCopy to write data from file to SQL Server and it yields few GiB/s of mem allocations.

1. Expected behaviour:
   char/byte buffer is created once per TDSWriter and reused on subsequent writes
2. Actual behaviour:
   char and byte arrays/buffers on every writeReader invocation
3. Error message/stack trace:
4. Any other details that can be helpful:

JDBC trace logs

Reproduction code

Call SQLServerBulkCopy#writeToServer many times

[ulvii]

Hi @vyaslav ,
Thank you for the contribution. The team will review the PR and get back to you.