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IDS Forum

Re: Informix HDR

Posted By: Ruben Dutan
Date: Thursday, 14 September 2017, at 9:51 a.m.

In Response To: Re: Informix HDR (Madison Pruet)

Great explanation
Saludos Cordiales

Fono: 2493452

On Thu, 2017-09-14 at 09:34 -0400, Madison Pruet wrote:
> You are mixing HDR a bit with logging mode.
> With logging mode set to UNBUFFERED the commit is not allowed to complete
> until the log containing the commit is flushed to disk. With BUFFERED logging,
> the transaction is allowed to commit without the commit log being flushed to
> disk. The log buffers are always written to disk in sequential order so that
> if the commit has been flushed to disk, then the entire transaction has been
> flushed to disk.
> With traditional HDR 'sync/async' mode was controlled by the setting of
> DRINTERVAL and had to do with the synchronization of the log buffer containing
> the commit and transmission of that log buffer to the secondary server. If
> DRINTERVAL was set to -1, then the log buffer would not be set to reuse until
> the buffer was sent to the secondary and acknowledged. Only then could the log
> buffer be reused. If DRINTERVAL was greater than zero, then the log buffer
> would be copied into an HDR transmit buffer and the log buffer would be
> immediatly reusable. The data in the HDR transmit buffer would be transmitted
> when it had aged DRINTERVAL seconds or whenever it became full, which ever
> came first. In both cases the acknowledgement occurred when log buffer was
> received on the secondary, not when it was applied.
> In more recent versions of the server, we added HDR_TXN_SCOPE which is used if
> DRINTERVAL is turned off (i.e. set to zero). This was done to decouple the log
> buffer from the transmission of the buffer. The reason was that by delaying
> the reuse of the log buffer had a negative impact on subsequent logging.
> Instead we coordinated the completion of the commit with the transmission and
> apply of logs on the secondary. If HDR_TXN_SCOPE is set to FULL_SYNC then the
> transaction completion is not returned to the client application until the
> logs of the commit have been applied on the secondary. If set to NEAR_SYNC
> then control is returned to the client application when the commit log record
> has been received on the secondary. If set to ASYNC then control is returned
> as soon as the commit log record has been copied to the HDR transmit buffers.
> In ALL cases the commit log record is processed on the primary server before
> any HDR work is done. It will be copied to the log buffer, written to disk if
> using unbuffered logging - and then enter HDR code.
> Now about what happens with a power failure on the primary. 1) Any logs in the
> log buffer will be lost. 2) Any logs in the HDR transmit buffer will also be
> lost.
> HDR compares the logs which have been applied on both the primary and the
> secondary when a reconnect occurs. This is done by comparing the LSN (log
> sequence number) of the most recent log written on the primary and the
> secondary. The LSN consists of the unique log file number + the position of
> that log within the log file. This way the primary will know what has been
> applied on the secondary and what it needs to send to get the secondary
> current with the primary. It will then transmit those logs from disk. Once the
> secondary is current with the primary, then the primary will start sending
> logs directly from the log buffers and HDR transmit buffers.
> Madison Pruet
> Retired and Loving it
> On Thursday, September 14, 2017 7:00 AM, MUKESH TANUKU
> <> wrote:
> Hi,
> I'm currently running Informix HDR (IDS 12.10FC8 on Windows server 2012 R2) in
> Async Mode. I just have a few questions:
> In Async Mode, the log is flushed to disk without waiting for a confirmation
> from the Secondary.
> What happens if a transaction is committed on the Primary and it suffers a
> failure (e.g. power outage) and the same transaction is still not committed on
> the Secondary (remains in Read-Only(Sec) mode)? When you bring up the Primary
> again, how does it know that it still needs to send the same transaction to
> the Secondary?
> What also happens if the log is not yet flushed to disk on the Primary and a
> sudden failure happens? What will happen to those "dirty" logs?
> Can anyone pls advise.
> *******************************************************************************
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> *******************************************************************************
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Messages In This Thread

  • Informix HDR
    MUKESH TANUKU -- Thursday, 14 September 2017, at 8:00 a.m.
    • Re: Informix HDR
      Madison Pruet -- Thursday, 14 September 2017, at 9:34 a.m.
      • Re: Informix HDR
        Ruben Dutan -- Thursday, 14 September 2017, at 9:51 a.m.
      • Re: Informix HDR
        MUKESH TANUKU -- Thursday, 14 September 2017, at 10:08 a.m.
    • Re: Informix HDR
      Marcus Haarmann -- Thursday, 14 September 2017, at 9:39 a.m.

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