From 50e0c749c1ad6df3b03f2e0528232f154db5d927 Mon Sep 17 00:00:00 2001 From: Tomas Vondra Date: Mon, 29 Sep 2025 21:17:20 +0200 Subject: [PATCH v20251001 07/25] improve BufFileCreateTemp/BufFileCreateCompressTemp comments --- src/backend/storage/file/buffile.c | 30 ++++++++++++++++++++---------- 1 file changed, 20 insertions(+), 10 deletions(-) diff --git a/src/backend/storage/file/buffile.c b/src/backend/storage/file/buffile.c index 88a1a30e418..6a43ad1ee38 100644 --- a/src/backend/storage/file/buffile.c +++ b/src/backend/storage/file/buffile.c @@ -206,13 +206,6 @@ extendBufFile(BufFile *file) * Note: if interXact is true, the caller had better be calling us in a * memory context, and with a resource owner, that will survive across * transaction boundaries. - * - * If compress is true the temporary files will be compressed before - * writing on disk. - * - * Note: The compression does not support random access. Only the hash joins - * use it for now. The seek operation other than seek to the beginning of the - * buffile will corrupt temporary data offsets. */ BufFile * BufFileCreateTemp(bool interXact) @@ -241,9 +234,26 @@ BufFileCreateTemp(bool interXact) } /* - * Wrapper for BufFileCreateTemp - * We want to limit the number of memory allocations for the compression buffer, - * only one buffer for all compression operations is enough + * BufFileCreateCompressTemp + * Create a temporary file with transparent compression. + * + * The temporary files will use compression, depending on the current value of + * temp_file_compression GUC. + * + * Note: Compressed files do not support random access. A seek operation other + * than seek to the beginning of the buffile will corrupt data. + * + * Note: The compression algorithm is determined by temp_file_compression GUC. + * If set to "none" (TEMP_NONE_COMPRESSION), the file is not compressed. + * + * Note: We want to limit the number of memory allocations for the compression + * buffer. A single buffer is enough, compression happens block at a time. + * + * XXX Is the allocation optimization worth it? Do we want to allocate stuff + * in TopMemoryContext? + * + * XXX We should prevent such silent data corruption, by errorr-ing out after + * incompatible seek. */ BufFile * BufFileCreateCompressTemp(bool interXact) -- 2.51.0